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2/19/2004
09:30 PM
Fred Langa
Fred Langa
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Langa Letter: Cool And Quiet, Part 1

Fred Langa finds ways to silence his PC's noisy fans while still keeping the PC well cooled.

I regularly get mail like this:

Hi, Fred, my cooling fans seem very noisy--I would guess a common complaint--but others I have heard in shops are WAY quieter. Why the difference? -- David [from Canada]

I know exactly what David means. I recently got a new PC that was extremely well designed in most ways, except that two of the system fans made a tick-tick-ticking noise that became extremely irritating. In fact, it eventually bothered me enough that I went looking for alternative low-noise replacement fans.

I was surprised to see how little top-quality fans can cost--often, they're only $7-$10 or so. I also found some extremely innovative heat-sink designs, and some rather unusual approaches to pumping heat out of a PC--quietly! By the time I was done, I'd found several excellent, low-cost solutions to excessive fan noise, and I now have a system that's literally whisper-quiet. It's a real pleasure not to hear it!

What's more, parts of my PC now run almost 20 degrees F/11 degrees C cooler than before, so not only is the system quieter, but it's better ventilated, too, which I expect will pay off in increased longevity and reliability.

And finally, along the way I also discovered some very interesting tools for monitoring and managing the temperature inside various parts of a PC. These tools--some free!--could be useful to you even if you're happy with your PC's current cooling setup because they can keep you better informed about your PC's health, and can even automatically act to avert disaster in the event that something eventually does go wrong.

Trade-Offs: Noise And Size Versus Cooling
We last covered fan noise and PC cooling two years ago (see "None Like It Hot"). Much of that article still pertains, and it's a good place to start if you're new to the whys and wherefores of PC cooling. But a lot has changed, too. For example, when that article was written, a top-of-the-line PC ran at 1.2 GHz, while my newest PC today clocks at 3.2 GHz. At speeds like that, a CPU pumps out a lot of heat.

The usual way to get rid of the heat is with one or more high-speed fans. Trouble is, the higher the fan speed, the noisier it is. The noise usually comes from three main sources.

First, there's the turbulent flow of the air itself--this is the white-noise "whoosh" normally produced by all fans. It's speed dependent: The faster the fan spins, the more energetic the turbulence, and the greater the airflow noise.

Second, the fan blades themselves also make noise as they slice through the air. Most of the noise actually comes from the tips of the blades, which are the fastest-moving part of the fan assembly. The faster the fan spins, the more noise the blade tips make.

Finally, there's the mechanical noise of the fan assembly itself. The motors and bearings in fans make at least a little noise, but cheap fans using needle or sleeve bearings make more noise than ball-bearing fans; and fans manufactured sloppily may suffer from vibration-inducing imbalances. All these noises get worse with speed: The faster the fan spins, the more mechanical noise it produces.

From the above, you probably already inferred the No. 1 rule for lowering fan noise: For lower noise you need slower speeds. Beyond that, careful design, superb manufacturing, and the use of top-quality components all will help, but the place to start is with lower speed because that instantly reduces all three major fan-noise components.

But there's a catch: If you slow down a fan, it won't move as much air, and won't cool as well. To maintain a given level of cooling--to move a given volume of cooling air--a slow fan has to be larger than a fast fan (everything else being equal). Likewise, a heat sink designed to work with low airflow volumes has to be larger than a heat sink designed for higher-flow volumes.

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