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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 . 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) . 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 . While
many relevant noise documents are designed to protect the health and safety
of workers ., 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
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 . 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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