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- March 4, 2007: Updated and substantially rewritten to reflect
the results of our fan test project
- August 26, 2004: Added info on comprehensive fan project
and added more fans to the list, including 92mm and 120mm models
- January 5, 2003: Minor changes
- December 24, 2002: First publication by Mike Chin
Silent PC Review has been interested in fans since its inception, way back
in 2002. This is no surprise — fans are the primary noisemakers in most
systems, and SPCR is a site about computer noise. However, for the first four
years of its existence, the vast majority of SPCR's fan knowledge was buried
in personal forum posts and the occasional mention of a particular "reference
fan". No formal fan reviews were done until November 2006.
The first baby steps towards reviewing fans occurred in early 2004, when we
announced a large scale project called Calling
All Good Fans — intended to be a comprehensive examination of the
best fans available. A quick glance at the list of updates above shows how long
this project took to bear fruit; this recommended list has languished for almost
three years as SPCR's knowledge of fans has stagnated. Now, at long last, the
project is well underway, and we are finally in the position to start recommending
fans on the basis of actual testing.
WHAT MAKES A GOOD FAN?
While there are numerous dimensions to fan performance, SPCR's recommendations
are based on just one: Noise. It's well known that the amount of noise a fan
makes is based largely on rotation speed, so it might seem that we should just
recommend the slowest fans available and leave it at that. However, that doesn't
quite cover what we mean when we say a fan has low noise. Thanks to the widespread
use of fan controllers, a fan's rated speed is almost irrelevant when
it comes to choosing a fan — computer fans are very rarely used at their
stock speed, especially in silenced systems that have been custom-built. Besides,
almost every fan on the market is too noisy to be considered at full speed.
Reducing the speed of the fans is a mandatory step in silencing a system.
Our recommendations assume that a fan controller will be used to reduce the
fan speed. When we evaluate noise, we base our conclusions on how a fan sounds
when it has been slowed down to an acceptable level. What is an acceptable level?
There are two rules of thumb here:
- A fan should be slowed down to the point where it provides just enough
airflow to prevent overheating.
- A fan should be slowed down to the point where there is no acoustic benefit
to reducing the speed further — i.e. the fan has become inaudible.
Both of these rules are system-specific; it is impossible for us to know what
the ideal speed for your system will be. However, long experience has
taught us how much airflow is needed in a well-built system, and our test procedure
reflects this: Fans are tested with the amount of airflow held constant: 10
CFM for 80mm fans, 15 CFM for 92mm fans, and 25 CFM for 120mm fans. A fan's
noise is judged based on how it sounds at this level, not how it sounds at full
speed.
Holding the airflow constant has the effect of reducing the acoustic difference
between various models. Most fans measure within a 2~3 dBA@1m envelope when
airflow is held constant, though this difference gets larger as fan speed increases.
At the levels we test at, the best fans are too quiet to measure — or
hear — from our standard measurement distance of one meter. What this means
is that our noise evaluations are based largely on how the fans sound subjectively. SPL measurements are useless when all of the candidates measure
below the noise floor of our lab — the measurements reflect the noise floor,
not the fan. Nevertheless, there are audible differences in fan noise, even when
they cannot be measured. A smooth, low hum is much more pleasant to listen to
than a sharp chattering whine, even if both are the same volume. If both are
below the ambient noise level, the sharp noise is much more likely to be audible.
The best fans — the ones we recommend — fade away entirely when slowed
down enough. Only a select few fans ever reach the point of inaudibility —
most fans remain faintly audible no matter how slowly they spin.
THINGS WE MEASURE
While our recommendations are based mainly on how the fan sounds at low speeds,
this is not the only thing we examine.
A detailed run-down of our test procedures and tools can be found in our
Fan Testing Methodology article, a summary of which follows below.
Brand vs. Manufacturer: Most readily available fans
come branded with a logo that identifies the company selling the fan. However,
as is so often the case in the tech industry, the company that sells the fans
is not always the same as the company that makes them. Where possible, we
identify the original manufacturer, as this can sometimes yield hints about
the fan's performance — or perhaps identify other fans that are similar
to the one being reviewed.
Bearing Type: Bearing type is an indicator of how long a fan will last, so we do our best to identify what type is used.
A word to the wise: The quality of the bearing is as important as the type of bearing. Unfortunately, things like reliability
and bearing quality are almost impossible to determine without looking at
hundreds if not thousands of samples. We leave you with bearing type, and let you draw your own
conclusions. Note that even among manufacturers, there is no clear consensus about which type of bearing lasts the longest; see the discussion about bearings by NMB and Comair Rotron in Anatomy of the Silent Fan.
Header Type: Fans are available with a wide range of connectors,
from bare wires to the complex 4-pin PWM headers that Intel brought to market.
Fans marketed to the PC community almost invariably come with either a 3-pin
motherboard header or a 4-pin Molex connection (or both), as these two headers
are almost universally supported. However, fans bought from surplus-sellers,
electronic shops, or eBay sometimes feature strange exotic headers whose original
use is often unknown.
There are a wide range of header types.
The Molex and the 3-pin motherboard headers (side by side in the center) are
the most common.
Starting Voltage: Extreme undervolting often involves
running a fan outside of its specified voltage, in which case it can be useful
to know how well the fan tolerates low voltages. A fan that doesn't start
consistently above 5V is generally looked down on, as many common fan controllers
give 5V as their minimum voltage. That said, most fans with problems starting
at 5V are slow enough that a higher voltage is desirable anyway.
Noise: This is why we test fans. Like every component
we test, fans are measured with a Bruel & Kjaer Model 2203 Sound Level
Meter from a distance of one meter. Noise is measured with the fan running
at 12V, 9V, 7V, 5V, and the constant airflow test mentioned above. Lengthy
subjective descriptions of the noise signature are also included.
Airflow: Airflow represents the cooling power of a fan. Our
measurements use an anemometer to approximate airflow, but aerodynamics is
too complex a field to be reduced to a single measurement with much precision.
Air pressure, which is closely related to airflow, and environmental
factors such as impedance are not taken into account. As a general rule, most
fans of a similar frame size generate the same amount of airflow (±10%)
at a given rotation speed, though drastically unusual fin or frame design
can break this rule.
Rotation Speed: This is a record of how fast the fan was spinning
during each test point — and it often serves as a reminder of how much
sample variance there is even within fans of a single model. 5~10% variances
between different samples of the same model are not uncommon.
Power: Power consumption is measured mainly as a point of comparison.
The vast majority of low speed fans (the ones that interest SPCR) consume
less than 2W at full speed, and less than 1W when undervolted to our reference
test level.
Sample Variance: Where possible, we try to examine more than
one sample of a given fan model, as sample variance is often quite high among
fans, especially for "minor" attributes such as noise. Not only
is good consistency between samples helpful for ensuring that you don't get
a bad sample, it is also an indication of good quality control at the factory.
One uncontrollable variance is that rough handling (like dropping a box of fans several feet) at any point during a fan's journey to SPCR (or the cumulative effects of many instances of rough handling) can cause subtle bearing damage that affects its noise. We always ask for the fans to be packed like thin-shelled eggs, but damage could have occurred before they're shipped to us. This type of damage may be subtle enough that very few users would actually notice and return or report such samples.
QUALITY AND RELIABILITY
Aside from noise, the most important factor to consider when buying a fan is
reliability. Unfortunately, build quality and reliability is impossible to test
without a long term study and a large sample size. Such testing is well beyond
the resources any free hardware review site, so we are limited to making educated guesses about fan quality. There are a number of factors that affect our
judgment of quality, some of which are listed below.
- Bearing type — ball bearings appear to last longer than sleeve bearings.
- Rated MTBF — how long the manufacturer thinks the fan will last. Not
all manufacturers are trustworthy in this respect, and interpreting what MTBF
means exactly can be challenging at the best of times...
- Manufacturer — some manufacturers are known to be better — or
worse — than others.
- Sample Variance — high sample variance suggests poor quality control,
and thus a higher chance of some kind of failure.
- General Build Quality — this covers everything from the type of plastic,
to the fit and precision of the molding, to the presence of "wobble"
while the fan is spinning. Basically, anything that appears to be out of the
ordinary is enough to raise our suspicions.
One thing to keep in mind that if you use fans the way we recommend — at reduced voltage and speed — they should last much longer than usual. With a decrease from rated RPM, there should be a proportionate increase in run time. It's possible that longevity is much less of a concern for quiet PC enthusiasts because we all run our fans much slower than they are rated for. Our own experience in the lab and with our own computers suggests this may be true. There have been very few fans over the last 5-6 years that we have found too worn out or become too noisy to remain in service; reusing old fans is a way of life for us.
OBTAINING LESS THAN 12 VOLTS
There are many ways of getting reduced voltage to the fan in order to run it slower and quieter.
• For those who want a simple control for a single 3-pin fan, a variable
voltage controller like the Zalman
Fanmate 2 is ideal. It is a small, inexpensive voltage controller with
a tiny knob that sits between the motherboard fan header and the fan, providing
a range of 5 to 11 volts. Cost is usually well under US$10. These devices
can also be built for as little as a couple of dollars if you are handy with
a soldering iron.
• A rheostat is a simple high power variable resistor that allows
fan speed to be controlled much like with a voltage controller. It is often
more expensive and less energy (heat) efficient than the potentiometer found
in most variable voltage controllers.
• For more elaborate, multiple fan control, products with names like fan bay, bay bus, and so on, are available. These generally occupy a 5.25" drive bay on the front panel of the PC case and allow control of 2 to a dozen fans, with a variety of features and options, including thermistor control. They range in price from US$10 to $100.
•
The 5V and 7V tricks: Do-it-yourselfers often tap into the voltage lines
available from any PSU. Three conveniently available voltages can be obtained
from the standard 4-pin Molex connector: 12V (yellow), 5V (red), and 7V (the
difference voltage between 12V and 5V). The 7V line is not really
that, and it is not recommended for more than one or two fans, especially
if they draw much power. For technical reasons we won't cover here, it can
cause damage to the PSU. For slow, low power fans, however, it is usually
perfectly safe with a good quality PSU.
• Switches can be configured for multiple voltage feed to fans
using the basic wiring information shown here. The DIY
12/5V switch is one example. There are many more variations that have
been described in the SPCR Forum and all over the web. Your imagination is
your main limitation.
• A simple way to get 6V is to wire two identical fans in series to 12V.
• Resistors in series (at least 1W rating) with the fan can also be used. 50~60 ohms usually provides around 5V from a 12V source. Adding ~25 ohms to 5V will give you around 4 volts. The numbers are approximate because the inductance/capacitance of the fan will affect the voltage drop.
• Zener diodes can also be used to reduce voltage — but
still allowing the full 12V to pass on startup.
USEFUL LINKS
In SPCR
On the Web
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