Fan

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Contents

Introduction

With modern PCs, the fans are the main sound source. Unfortunately, the dissipation loss of high clocked CPUs, graphic cards and other parts forces one to transport the heat out of the case. Nearly all of the output of the power supply is dissipated as heat and has to be taken out of the case, either by air flow or water cooling.

The normal convection of heated air is not enough.

Heat sources

The hottest parts of a modern computer system

  • CPU, dependend of the type it ranges from 8 Watt to 115 Watt(P IV 3.8GHz Prescott)
  • power supply, ca. 90..95% efficiency outcomes up to 20 Watt
  • DVB card, ca. 8 Watt (Fujitsu-Siemens DVB-C FF)

Other heat dissipating components

The quiet PC

The most efficient abatement of noise is the abandonment of all sound sources. Therefor unnecessary high clock rates should be avoided and low current components should be choosed over normal ones. Only then low noise fan makes really sense.

The loadness of a fan depends on

  • Size
  • Rotation speed
  • Flow rate
  • Bearing
  • Aerodynamics
  • Fixation type (structure-borne sound)

Fans are avaible in the sizes 35, 40 50 60 80 92 and 120 millimeter. Smaller fans must have a higher rotation speed for acceptable flow rates and hence are loader than bigger ones with lower rotation speeds. A good tradeoff are 80mm fans.

Normally fans are driven with 5V to 12V. Higher voltage results in higher rotation speed and more noise. Therefor 12V fans are often driven with only 7V.

Warning
Warning

When reducing the voltage, check that the fan can really start at the new voltage level.

Also be aware of the fact that the fan has now a lower flow rate with less cooling capacity.

The compromise are fans that are

  • temperature controlled
  • have good bearings (Ceramics, e.g. Papst)
  • 80-120mm in size
  • decoupled from the case

Fans known to be quiet

  • YS-Tech FD1281251B-2A: 17dBa, 40m³/h, 80x80mm, ca. 4Euro at EBay, very low noise at 9V
  • Papst 8412 NGL (Hungary): 12dBa, 33m³/h, 80x80mm, ca. 10Euro
  • Noiseblocker Silent Fan S1: 11dBa, 38m³/h, 80x80mm, ca. 12Euro

Useful accessories

  • Decoupling set for fans, also offered as "Fan Silencer": ca. 2Euro per 4 apiece

Links

[1] www.silentpcreview.com Comparison of more than 100 fans at 12V/7V/5V
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