Computer Noise in the 21st Century

The Silent Front
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The Present
Over the past few decades, many electronic system design groups have incorporated noise control measures into their products. The primary design changes were the integration of fan speed control, system flow impedance reductions and improvements related to air-moving device inflow/outflow conditions [1]. It is not unusual for such changes to provide 1-2 bels (10-20 dBA) of noise reduction.

When designing telecommunications or information technology equipment, manufacturers rely on a variety of benchmark documents. For the telecommunications industry, one such document is a recently published standard created by the European Telecommunications Standards Institute (ETSI) [3]. The ETSI document specifies a set of sound power limits for equipment sold in Europe. Similarly, a few individual countries have produced similar documents for the computer and business equipment industry.

For example, the Swedish Agency for Administrative Development (Statskontoret) produced one of the first of these several years ago [4]. While many relevant noise documents are designed to protect the health and safety of workers [5]., the European documents are principally intended to ensure that equipment does not excessively impact speech communication, task concentration, and other perceptual factors in spaces where equipment is installed. In general, the limits in these documents have not been primary design drivers for manufacturers since the limits could often be met using conventional noise control techniques. As a result, noise emission has usually been a relatively low-priority design issue.

The Future
With very few exceptions, the general trend in telecommunication and information technology system design has been toward increasing heat loads. Consequently, for systems that must be cooled using forced-convection, noise emission is also rising. These trends are driven primarily by customer demand for increased system throughput, and decreased enclosure size [6,7]. For these industries, the dramatic increase in Internet access has rapidly driven data rates up.

Over the period from January, 1996 to January, 1997, the number of addressable Internet domains quadrupled [8]. Soon, as convergent systems become widely deployed, single networks will carry data, voice and video. The speed at which these changes will occur is likely to mean that many design assumptions and specifications will need to be constantly revisited. System power (i.e., heat) dissipation is driven by performance trends at both the integrated circuit and printed wiring board level. The next two sections discuss trends in chip and board design, and the likely effects on noise emission.

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