|Noctua ANC Project|
Active Noise Cancellation (also referred to as Active Noise Control or Active Noise Reduction) is the technique of using sound waves to reduce noise by means of an effect called phase cancellation or destructive interference. When a noise signal is superimposed by a sound signal with the same amplitude but inverted phase, the two waves effectively cancel each other out.
Effective cancellation can usually only be achieved in controlled environments (e.g. noise-cancellation headphones or car interiors) and at specific positions because the original signal and anti-signal have to be matched precisely in inverted phase and amplitude in order to cancel each other out. Axial fans pose the extra challenge of producing rotating pressure fields that exhibit a highly complex phase structure and are thus very difficult to cancel out using ANC.
The patented RotoSub® ANC technology allows the fan itself to emit the anti-noise signal through minute modulations of the fan blades, which are achieved by switching on and off a coil within the fan frame that interacts with magnets inside the blade tips. This way, the anti-noise comes from the exact same position as the original noise and precisely matches its phase and rotation pattern. Thanks to this, the cancellation effect achieved through RotoSub® ANC technology is omnidirectional and largely independent from the environment.
First test results with a 2500rpm Noctua NF-F12 120mm fan prototype with integrated RotoSub® ANC confirm a significant reduction of tonal noise components. The development goal is to achieve a more broadband sound signature that sounds more agreeable to the human ear.
The suppression of tonal noise components can also be observed in a demo-video that shows ANC being switched on and off on the NF-F12 prototype: