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This January 1999 article originally entitled Acoustic Noise
Emission and Communication Systems in the Next Centuryis reprinted
with permission of the author Dan Quinlan, of Lucent Technologies, and the publisher,
Cooling, a magazine about thermal management in the electronics industry.
It remains relevant to silent PC enthusiasts today. Mr. Quinlan documented the
trend towards greater heat in telecom & computer equipment, leading to increased
use of cooling fans and more noise, possibly as much as 10-20 dB in the next
Within a few months of the article's publication, the first AMD K7-500
burst on the scene, with a then-unheard-of 42W maximum power dissipation, some
35% higher than a similarly clocked Intel P3. Based on personal experience with
PC upgrades, Dan Quinlan's prediction of at least 2 dB/year noise increase for
the next decade is right on the money so far; I don't need test gear to tell
me that my latest 2 GHz system run in stock form is easily 6 dB louder than
what I was using in January 1999. If any of the new 50+ cfm fan equipped CPU
heatsinks were used, the increase would easily exceed 12 dB.
Mr. Quinlan has been working on a very different set of problems since
then, but has a more hopeful view today: My guess is that the graph might well
look different since the chip industry seems to have put alot of effort into
lowering power dissipation. Manufacturers of laptops, PDAs, and cellphones have
been applying plenty of pressure to make improvements. For those industries,
power is a major issue. Whether this translates to noise reductions in PCs as
well remains to be seen.
Forward by Mike Chin, April 11, 2002
Acoustic noise emission is one of several physical design issues addressed
during the design of telecommunications and information technology equipment.
In most systems, noise is a by-product of the air-movers used for system cooling.
The amount of heat dissipated in electronic systems cooled by forced convection
is directly proportional to volumetric flow rate. The flow rate, in turn, is
directly proportional to the rotational speed (N) of the air-mover. Dimensional
analysis and laboratory measurements have shown that when the rotational speed
of a typical air-moving device increases by a factor of , the corresponding increase in the sound power level, Lw(in bels), can be estimated using:
Lw = A log (n)
where 5.0 <= A <= 5.5 . For reference,
a relatively quiet system will have a sound power value of 3.5 - 4.5 bels, whereas
emission levels above 7.0 bels will result in local sound pressures that will
be considered to be quite loud, or even harmful at higher levels. In the world
outside electronics, a vacuum cleaner might be near 7 bels while a jet engine
might be near 15 bels .
Given the strong dependence of noise level upon heat dissipation,
trends in noise emission are inextricably related to developments in integrated
circuit and printed wiring board design. The intent of this paper is to briefly
discuss projected trends in chip and board design, and then assess the impact
on noise emission.
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