Archive: A Primer on Noise in Computing

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HEALTHY NOISE LEVELS

It's well known that long exposure to noise levels above ~70 dBA can cause noise-induced hearing loss. There is also considerable recent evidence that much lower levels of noise have a real impact on learning, stress, and productivity.

Cornell University researchers published a study in the Journal of Applied Psychology in 2000 on the effects of what would be considered moderate levels of noise on workers in the common open-office environment. They found that there was psychological, motivational, and observational evidence of elevated stress. They concluded that chronic exposure to even low-intensity noise may have the potential to cause serious health problems such as heart disease (due to elevated levels of epinephrine, a stress hormone) and musculoskeletal problems.

Workplace stress is no joking matter. The Confederation of British Industry (1992) estimates that, in the UK, 360 million working days are lost each year through illness. The Health and Safety Executive calculates that at least 50% of those lost days are due to stress.

The US Federal agency National Institute for Occupational Safety and Health (NIOSH) identifies job stress as a major cause of ailments and productivity loss, and lists noise as one of the main contributors to workplace stress.

A comprehensive 1999 study for the World Health Organization recommends:

"In schools and preschools, to be able to hear and understand spoken messages in class rooms, the sound pressure level should not exceed 35 dBA during teaching sessions."

The WHO study specifies the same maximum level of 35 dBA for the interior of homes, to "maintain comfortable speech intelligibility and avoid annoyance." While no comparable recommendation was made for office environments, it is easy to see how the mentally challenging work conducted in many offices is similar to that done in classrooms, and there is no reason why a similar standard for maximum noise in the work environment shouldn't apply.

One other simple fact is that noise begets more noise. If the background noise is low, then people speak softly and communicate well whether in person or on the phone. As the ambient noise level increases, people speak louder in order to be heard. When the background noise in an open-office is high, then everyone speaks louder, and the overall noise level is far higher than in a quiet ambient.

In short, the intuitive knowledge most of us have that a quiet environment is conducive to reduced stress, improved learning, higher productivity, and finally, better health, both mental and physical, is confirmed by scientific authorities.

COMPUTER NOISE

Cooling fans (in the power supply, the CPU heatsink, motherboard chipset, VGA card and the case itself), hard drives and optical drives are the noise sources in typical PCs. Typical current PCs emit 3.0 to >5.0 bel sound power . Even PCs at the bottom of this noise range (3.0 bel) can be heard in a classroom, office or living room because:

In a classroom or office, it's rarely just one PC but rather, at least several and often dozens; in concert, even 3.0 bel PCs clearly become a source of noise. In a living room, the ambient noise is often low enough that it does not mask that level of noise.

PCs closer to the middle of the range, say 4.0 bel, are easily heard in most class, office or home environments.

Realizing that system noise is an important issue, hard drive manufacturers have already fully embraced sound power as a noise declaration standard. Large PC makers are also becoming slowly aware of noise. Dell and HP both began in mid-2002 to include sound power and sound pressure data in the specifications for some of their PC systems, although this information still requires digging on their web sites to find. The vast majority of PC makers do not have consistent standards for noise emission declaration.

WHY SUCH NOISE LEVELS IN TYPICAL PCs?

The relationship between computing power and noise is not direct, but closely related. As the central processing unit (CPU), random access memory (RAM), the hard drive (HDD) and other components run at faster speeds, they inevitably emit more heat. The most cost-effective way to cool hot electronic components is with heatsinks and fans.

The CPU is the toughest cooling challenge, because it produces so much heat in such a small area. The core die of a typical modern CPU is no bigger than one square centimeter, yet some Intel P4 variants have already exceeded 100W heat dissipation. The heat density is incredibly high! Large copper heatsinks with high-speed fans have become virtually mandatory in powerful desktops for this very reason. Add to that the processor found in modern VGA cards, which are now approaching 75W.

The amount of heat generated inside a PC is generally evacuated by cooling fans. Small DC fans are the cheapest way to remove heat from a PC.

An Aside: To be fair, these wattage numbers represent the most conservative estimate of system power requirements, as they are the very highest peak levels that can be reached with a system of comprised of these components. In typical usage for desktop applications, average power is usually 50% of the numbers cited. Consider the discussion here most relevant for worst-case scenarios. Still this is the approach that AMD and Intel both take to estimating power needs. Also, the document in question is 18 months old; both VGA and CPU power dissipation have jumped ~50% since then.

An AMD document, Builders Guide for Desktop/Tower Systems, suggests that the total power for a typical system based around their XP1800+ processor "needs a power supply of at least 162.47 W." The same document calculates that a "High Performance" system based on their XP2100+ processor "needs a power supply of at least 241.91 watts." This AMD document is being cited, but the numbers for Intel processors are just as high, in fact, even higher as their P4 processors ramp up beyond 3.0 GHz clock speed.

The AMD XP1800+ processor has a typical power dissipation of 60.7W, is similar to the 61W rating of the Intel P4-2.5G; the AMD XP2100+ processor has a typical power dissipation of 64.3W, similar to the 66.1W rating of the Intel P4-2.67G. There is little reason to doubt that the Intel CPU of similar speed rating in similar systems would have power supply requirements very similar to the aforementioned AMD systems. Keep in mind that none of these processors are the fastest and hottest of either line at this time.

Whatever power is drawn by the components is dissipated as heat. The power supply mentioned above also produces heat. We can safely say that power supplies used in desktop systems have an average AC/DC conversion efficiency of about 65%. Of the AC power drawn by the PSU, 65% is delivered to the components as DC power; the remaining 35% is lost as heat within the power supply itself. The following table shows this simply:

Type of system DC Power Lost in PSU Total AC Power
Typical XP1800+ 162.47 W 87.55 W 249.95 W
Performance XP2100+ 241.91 W 130.26 W 372.17 W

The total amount of power used by the system may or may not surprise you. What is really interesting:

Total AC Power is a very good estimate of the total heat generated in a PC.

Even if a relaxed approach to power requirement is taken, and the total AC power numbers are dropped by 50%, we're still looking at 125~185W of heat in the case. It's not a surprise that conventional PCs make as much noise as they do, given the airflow required to remove all that heat!

The noise from fans is exacerbated by case and system designs that fail to provide optimized airflow paths to maximize the cooling power of those fans. High airflow impedance invariably causes higher noise from fans and from air turbulence.

MONKEY NO HEAR

All this is part and parcel of the general prevailing attitude in the industry that, somehow, noise is not an issue, and more importantly: Quiet is not a sellable feature.

Simple things such as soft mounting of hard drives, optical drives and fans that can dramatically reduce noise have routinely been ignored -- as have 90% of the quieting solutions considered, discussed and formulated in the pages of Silent PC Review (SPCR). It's only in the past year or so that manufacturers have begin to notice the noise made by silence seekers. While there has been a increase in the number of genuinely useful quiet components, the number of dubiously marketed so-called silent products has also mushroomed, and quiet prebuilt PC are still hard to find. The enthusiasts at SPCR remain far in advance of the industry in finding and implementing solutions to reduce PC noise.

The single most important reason that PCs are not quieter is that management has not demanded engineering to consider low noise as a primary goal. I wrote in the article The State of Computer Noise: January 2003,

Given what do-it-yourself enthusiasts can achieve with just creativity, desire and minimal funds, it seems clear that if the industry focused its enormous resources on the noise issue, it could be solved overnight at minimal cost to them or to the consumer.

In a broad industry-wide sense, until management and sales are convinced that a quieter PC is a more sellable PC, we will not see this shift in focus. Some individuals, some divisions and maybe even some entire companies in the PC industry are beginning to hear and listen. We'll see how long it takes for the entire industry to uncover their ears.



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