Hardware & Infrastructure
11:46 AM
Fred Langa
Fred Langa

Langa Letter: Cool and Quiet, Part II


In Cool and Quiet -- Part One, we started with the basics of quieting a PC's noisy fans. We then saw how PC noise reduction can actually be rather easy, and cost just a few dollars. We discussed how fan speed is the No. 1 variable in PC noise, and how air turbulence, the tips of a fan's blades, and plain mechanical noise all contribute to total fan noise. Slowing down a fan--or replacing a fast fan with a slower-turning one--reduces all these noises.

But we also saw how cooling efficiency falls off as air flow decreases: If all you do is slow down your PC's fans, you'll raise your PC's internal temperatures, and that's not good at all. Heat is the enemy of electronic components, and overheating can destroy or shorten the life of your system. So, anything you do to quiet your PC must not compromise its cooling.

Fortunately, as we discussed, there are excellent, 100% free tools to assist you in avoiding costly cooling mistakes--like a fried CPU. Some of these tools even actively intervene to keep your PC safe in the event of a thermal problem.

By the end of Part One, we saw how the right knowledge and some free or low-cost software and hardware will let you eliminate much of the noise your PC makes, without causing cooling problems. In fact, when I was done modifying my own brand-new 3.2GHz Pentium 4 PC, it ended up literally whisper-quiet and actually runs cooler than it did in its original factory configuration. Cool and quiet--the best of both worlds.

If you haven't done so already, please read Cool and Quiet--Part One now, as it contains essential background and additional details that make this article--Part Two--make sense.

More Is Less
For me, the key to understanding how to quiet my PC was is in this seemingly contradictory statement: You actually can quiet your system by adding more fans than it came with from the factory. It's totally counterintuitive, but we'll show you how it's true: Several slow, quiet fans can easily be quieter than one fast, noisy fan.

There are hundreds of PC fan types available, but only a few cater to sound-sensitive PC users: The manufacturers and retailers of these fans will prominently list two important variables: a sound measurement (in decibels, or dB) and an airflow rating (in the USA, in cubic feet per minute, or CFM).

The airflow rating is easy to understand: Everything else being equal, a fan that moves more air is better for cooling than one that moves less air.

The sound or decibel rating seems straightforward, but it isn't. Yes, the lower the dB rating, the lower the noise; and all else being equal, you'll want the quietest (lowest dB) fan that will move the volume of air you want.

But the decibel scale gets confusing because it's not linear. In geek-speak, a decibel is a unit of acoustic power equal to 10 times the logarithm of the ratio of one sound to another.

What that means is that small changes in decibel ratings make a huge difference: The decibel scale is designed so that each change of 10dB on the scale represents a tenfold change in acoustic power, which to a normal human ear sounds roughly like a doubling or halving of the volume.

This pays off big time when you're fan shopping. For example, if you remove a typical 30dB system fan and replace it with a same-sized 20dB fan (which you usually can buy for under $10), the new fan will seem only half as loud as the old.

That sounds great (so to speak) but that 20dB fan will almost surely move less air than the original 30dB fan, so you'll lose some cooling power.

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