While it doesn’t quite match up to the fanless heatsink in terms of efficiency or straight-out awesomeness, the self-muffling RotoSub is certainly right up there in terms of ingeniousness. If you want to skip right to the goodies, scroll down to the embedded video below, otherwise read on for an explanation of how RotoSub technology actively cancels its own noise.

You have probably heard of noise-canceling headphones, and RotoSub’s approach is fundamentally quite similar. In the case of active noise control headphones, a microphone measures any external/background noise and then plays the “anti-sound” (the inverted phase) through the headphones, effectively eliminating these noises. This technique could be used with fans, but you would need to put speakers both in front and behind the fans to emit the noise-canceling sounds — and even then, this approach only works if you are directly in between the fan and the speaker. Not to mention, such an approach would be complex to wire up.

RotoSub puts active noise control inside the fan itself. Unfortunately, RotoSub doesn’t actually say how this new technology works — but considering RotoSub makes its money by licensing the technology to other companies, perhaps it’s wise that they don’t give away all of their tricks. RotoSub’s CEO has given CNET a few tantalizing hints, however: by modulating the angle of attack of the blades, RotoSub generates “the same phase structure as the noise, the same position, and radiation pattern.”

Judging by an image on the RotoSub site (above), it looks like there’s a metal track around the outside of the fan. Perhaps this track is used to measure the fan’s rotational properties in some way? Or maybe it provides a small amount of electricity to “modulate the angle of attack of the fan blades”? There is also some control circuitry attached to each fan — you can see it being enabled and disabled in the video below), so presumably some kind of real-time signal processing could be used to produce inverted-phase sound waves. This circuitry apparently uses very little power, too — though no exact figures are given.

Beyond silencing computer fans, RotoSub’s R-ANC (active noise control) technology could also be applied to just about any kind of fan, including ventilation/air conditioning systems, and even the turbofans on the front of airplane jet engines.

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