Silence your PC

Posted at: Friday 7th October 2005 by James Morris

A powerful PC doesn't necessarily have to sound like a jet engine. James Morris investigates how to make a high-end PC more acoustically demure

A hotrod car is meant to be noisy. After all, what street credibility would a TVR have if it didn't make a throaty roar like an angry tiger? PCs are different though. Outrageous modding and lighting might make a statement about your PC, but it isn't one that you want to hear as well. If your PC is too loud, then you might miss that monster creeping up behind you in Doom 3, and you'll ruin the nuances of your finely balanced 7.1 surround-sound system too.

If your PC was built for speed, then the chances are that it's full of humming fans and fast-revving hard disks chugging away. But does it have to be this way? High-performance components usually emit more heat, which means that they require more effective (and noisier) cooling systems. However, as Intel's Pentium M shows, you can have your cake and eat it. What's more, you can still have your cake and eat it with a high-end Pentium 4 or Athlon 64 gaming system.

A sensible choice of supporting components could give you all the gaming frame rates you desire, and without any sonic pollution. Noise has become such a huge issue for PCs in recent times that a whole industry has sprung up to take some of the pain away. Alternative coolers, matting kits, fan controllers and hard drive enclosures are all readily available to help reduce noise, but which of these options have the biggest impact?

We put a few of them through their paces to find out. We built a standard high-performance gaming PC and took it along to the environmental testing specialists at Intertek for sound testing. We then tried out a series of components designed to cut down the hullabaloo, and then built a quiet PC to see what the overall difference would be. Read on to find out what we discovered.

Bring the noise

Before we get down to the nitty-gritty of testing, however, let's take a tour of sound measurement. The most common unit you'll see for measuring the volume of a computer component is the decibel (dB). However, the decibel is actually the ratio between two quantities and doesn't necessarily just refer to sound level. It's also used for relative voltage levels. Named in honour of Alexander Graham Bell, the bel is equal to the reduction in audio level over a one-mile length of standard telephone cable, so it clearly refers to both acoustic and electrical elements.

For measuring PC noise, however, the bel is too large a unit, which is why we use decibels instead, which are one-tenth of the size of the bel. The decibel is a measurement of sound pressure level and, as it's a relative measure, it's defined in relation to the threshold of human hearing, which is conventionally 2 x 10-5 N/m2 (where N = Newtons). However, the bel is a base ten logarithmic scale, so 20dB doesn't represent twice as much sound pressure as 10dB, but ten times as much.

Fortunately, the Weber-Fechner law states that human sensory perceptions also follow a logarithmic scale, so 20dB would sound twice as loud as 10dB to the human ear, even if the sound pressure is ten times that amount. Incidentally, 10dB is similar to the sound level of a person breathing when heard from 3m away.