Quiet Computing From VIA - Why is Noise a Problem

The hum of your fan and the whine of your hard drive do more than just distract from the movie you're watching. In network environments like offices and school computer rooms the background noise level from PCs and Servers can reach between 50 and 60 decibels, similar to standing next to a busy road.

A high level of background noise can have serious detrimental effects on performance and productivity. Various studies have been carried out to determine the negative effects of PC noise on office productivity and stress in the work place:

1) A 1998 report published in the British Journal of Psychology found that excessive noise can diminish the performance levels of office workers by as much as 60 percent.

2) A 2000 report in the Journal of Applied Psychology by a Cornell University Research Team² that detailed the specific negative effects of low intensity office noise. They found that stress levels were significantly higher in an office with low intensity background noise than in a quiet office. This can adversely impact the health and well being of office workers. The study group also showed less motivation in approaching problem solving tasks, seriously affecting productivity.

3) The Confederation of British Industry (1992)¹ 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.

4) The US Federal agency National Institute for Occupational Safety and Health (NIOSH)¹ identifies job stress as a major cause of ailments and productivity loss, and lists noise as one of the main contributors to workplace stress.

The negative effects of PC noise also extend into the classroom as PCs play an increasingly ubiquitous role in education. 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."³

The WHO study specifies the same maximum level of 35 dBA for the interior of homes, to "maintain comfortable speech intelligibility and avoid annoyance."

The demand for solutions to this problem is growing and much of the PC industry's limited resources are being directed at making the necessary huge power supply and CPU coolers quieter. VIA's cool running processor platforms are developed to solve the problem at the source by generating as little heat as possible and reducing the need for high speed and noisy processor, power supply and case cooling fans. Highly efficient VIA processor platforms not only require less forced air cooling from fans, they also require less power from the power supply, so a quieter, smaller power supply can be used. The combination of a cooler CPU and power supply results in less need for overall system cooling from case fans, and so the whole PC can be made cooler and quieter, simply by using a cool running processor.

Main Causes of Noise in a PC

The main noise sources in typical PCs include:

» Cooling fans (in the CPU heatsink, the power supply, the motherboard chipset, the VGA card/GPU and the case itself).
» Hard disk drives.
» Optical drives.

Current typical PCs emit 3.0 to >5.0 bel sound power¹. Even PCs at the bottom of this noise range (3.0 bel) can be heard in a classroom, office or living room because:

1) In a classroom or office, it's rarely just one PC but at least several and often dozens; in concert, even 3.0 bel PCs clearly become a source of noise. Two PCs producing 3.5 bel of noise will add up to 3.8 bel; four such PCs will make 4.1 bel; eight will make 4.5 bel and 16 will make 4.8 bel. Ten identical PCs emitting 3.5 bel will add up to 4.5 bel¹.

2) In a living room, the ambient noise is often low enough that it does not mask that level of noise.

PC Noise Measurement Comparisons

Noise is generally measured in decibels (dB) which is a complicated logarithmic scale rather than a linear scale. As a simple guide, a 10dB difference is generally perceived by the human ear as being twice or half as loud. This means, for example, that if one source of noise is measured at point of perception at 85 dB, another source measured at 75 dB sounds half as loud. A 95 dB source sounds twice as loud as the 85 dB source, and four times louder than the 75 dB source.

The following table shows Sound Pressure Levels for common sounds as a frame of reference to PC noise levels¹:

PC noise consists of non-pure tones that are basically many tones in complex combinations of frequency, amplitude and timing. Human hearing sensitivity varies with frequency where it is less sensitive in the high and low frequencies, and more sensitive in the mid-range frequencies. The "A" weighted scale was developed to compensate for the irregular frequency response of human hearing and "A" weighted decibel readings (expressed in dBA) provide a more fair comparison of relative loudness.

A calibrated Sound Level Meter (SLM) and sound power measurements of the Hush Silent Mini-ITX PC being taken in an anechoic chamber (right).

The decibel (dB) is the measure of sound pressure level (SPL) and is most commonly used to measure PC noise (as dBA) because it is relatively simple to perform these measurements. SPL measurements can be seen as a single snapshot photograph of a particular PC from one angle and is achieved through pointing a single microphone at the system while it is running and recording the noise reading.

Sound power is a more complete measurement of PC noise that expresses the total amount of acoustic energy emitted by a system. It can be seen as a 3D image compiled from many photographs around the PC and is achieved through placing multiple microphones from many positions around the sound source and calculating a noise value from all the microphone readings. Sound power is a more accurate measurement of noise under a wide range of environments, and correlates better with human perception, especially for comparative purposes.

To distinguish sound power from SPL, it is commonly expressed in bel (a decibel is 1/10th of a bel). The A weighting scale is also generally applied to sound power measurements.

For information on how to test PC noise yourself, download this simple guide by SilentPCReview.com.

How to Reduce Noise

Here are a few suggestions that will help make your system silent or at least quieter.

1. Use a cool running VIA processor platform with a small and quiet fansink or even a passive cooler; VIA recommends the VIA EPIA Series of Mini-ITX mainboards.
2. Use a quiet power supply with a low voltage cooling fan with RPM that changes with the temperature inside the case.
3. Use quiet drives
4. Use larger quiet fans, with lower RPMs.
5. Use fans that adjust speed according to the temperature inside a case.
6. Use enclosures (sound absorbing box/sleeve) for hard drives to muffle the hard drives.
7. Use a sound absorbing material to line the inside of the case.
8. Seal off the case with materials such as foam and rubber.
9. Put the CPU box inside a cabinet.
10. Use rubber washers and separators at key areas where transmission of vibration may cause noise, like in fan and drive mounts.
11. Mount your system on rubber or carpet "feet".

Resources

For more information on computer noise, or to download the Noise, Computing and VIA whitepaper, check out these resources:

Find an extensive list of quiet components at SilentPCReview.

Other Quiet Computing Links

Remember that many noise reducing steps, like adding additional noise absorbent materials inside your casing, can help to heat up your system. We believe that keeping a PC cool goes hand in hand with keeping a PC quiet, so do the sensible thing and get into "cool processing".

References

¹ "Noise, Computing and VIA", Mike Chin, editor/publisher of SilentPC Review, May, 2003
² "Stress and Open-Office Noise", Gary W. Evans and Dana Johnson, Cornell University, Journal of Applied Psychology, 2000, Vol. 85, No. 5, 779-783, ©2000 American Psychological Association.
³ Guidelines for Community Noise, edited by Birgitta Berglund , Thomas Lindvall, and Dietrich H Schwela ©World Health Organization 1999: http://www.who.int/peh/noise/guidelines2.html
From 'Table 4.1: Guideline values for community noise in specific environments' in 'Chapter 4: Guideline Values'. The actual noise term specified was LAeq(16hrs); LAeq = Equivalent Continuous Noise Level. The noise level in dB(A) which if present for the entire measurement period would produce the same sound energy to be received as was actually received as a result of a signal which varied with time. Normally abbreviated to "Leq" or "LAeq", often followed by a specification of the time indicating the period of time to which the measured value has been normalized; for example, "LAeq(8hr)".