Self-Silencing Cooling Fans
If you've ever been driven completely mad by the sound of one of your PC's cooling fans you'll certainly appreciate the improvements a Swedish company called RotoSub has made to them. While it can't eliminate the sound of the air rushing through the blades, their R-ANC (Active Noise Control) technology effectively deals with sounds generated by the fan's mechanical moving parts, which typically are the annoying culprit.
Normally, noise cancelling technologies use a microphone and a separate speaker to generate sound waves that are out-of-phase with the sound being eliminated. And as the two signals combine, they effectively cancel each other out. From what I can tell the R-ANC technology works in a similar fashion, except that instead of a speaker, the noise-cancelling out-of-phase signals are generated by the blades themselves as their "angle of attac" is modulated ever so slightly.
Source: ohgizmo.comAdded: 12 August 2011