Computer Noise in the 21st Century

The Silent Front
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Conclusion
Power dissipation data clearly points toward increasing thermal loads for telecommunication and information technology systems. This rise is occurring because the drive toward higher system throughput with decreased cabinet footprint is stronger than the drive toward reduced power consumption. As these heat loads rise, there will be a corresponding increase in acoustic noise emission. The design trend data indicates that noise emission is likely to rise by 1-2 bels (10-20 dB) over the next five-to-ten yeaqs.

Given the proliferation of desktop workstations, it is also important to note that fans in these systems control the background noise levels in many office environments. While people have grown accustomed to this added noise, the negative effects of fan noise will likely become more apparent as hands-free desktop conferencing becomes more widespread. Very little noise research has been done on small cooling fans since they are low-margin commodity items.

However, it is clear that the conventional techniques will soon be inadequate. While active control may seem at first to be a promising solution, there are several technical and financial problems that may be impossible hurdles [11]. So, new approaches to noise reduction will probably come from radical changes in cabinet design unless a concerted effort is made to initiate research on the basic understanding of the noise generation mechanisms in small air-moving devices [12].

The above discussion assumes that systems will continue to be predominantly cooled using forced-convection. Despite the fact that other thermal management technologies exist, forced-air cooling will remain the predominant technique because it is relatively cheap, highly reliable and designers are well versed in its use. However, given the dissipation trends in chip design, it is clear that hybrid designs that couple forced convection system cooling with "local" cooling of high dissipation chips will become more common. It may be that local cooling technologies such as spray cooling, jet impingement, heat pipes, thermoelectric cooling, and liquid cooling may finally see more widespread use.


Acknowledgments
Many people within Lucent and other organizations have been kind enough to provide assistance during the preparation of this paper. The author is grateful for their input and cooperation.
D.A. Quinlan
Bell Laboratories
Lucent Technologies Inc.
101 Crawfords Corner Way, Rm 1H-511
Holmdel, NJ 07733-3030, USA
Tel.: 732-332-5386
Fax: 732-949-8797
Email: dbq@lucent.com

References
1 G.C. Maling, "Historical developments in the control of noise generated by small air-moving devices," Noise Control Engineering Journal 42(5), 159-169 (1994).

2 L. Beranek and I. Ver, Noise and Vibration Control Engineering, (New York: Wiley-Interscience) 1992.

3 ETSI ETS 300 753,  "Equipment Engineering (EE): Acoustic noise emitted by telecommunications equipment."

4 Statskontoret Technical Standard 26:2, "Noise of computer and business equipment."

5 U.S. Occupational Safety and Health Administration (O.S.H.A.) 29 CFR 1910.95 (CFR=Code of Federal Regulations).

6 C.J.M. Lasance, "The need for a change in thermal design philosophy," Electronics Cooling 1(2), 24-26 (1995).

7 W. Aung, Cooling techniques for computers, (New York: Hemisphere Publishing) 1991.

8 "Runaway Internet Growth," NetworkWorld 14(11), 1, 1997.

9 D. Tilton, A. Partha and F. Borchelt, "Advanced thermal management for multichip modules," Electronic Packaging and Production (1995).

10 Semiconductor Industry Association, The National Technology Roadmap for Semiconductors (1994).

11 D. Quinlan, "Application of active control to axial flow fans", Noise Control Engineering Journal 40(1), 95-101 (1993).

12 D. Quinlan and P. Bent, "High frequency noise generation in small axial flow fans," Journal of Sound and Vibration (in press - 1998)

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