The three P's

There are three key properties that are essential in all active noise cancelling applications.

  • Power
  • Phase
  • Position

Without addressing all of these, it is not possible to achieve good attenuation of all noise frequencies, in all directions. Specifically for a fan, the solution must be able to suppress noise upstream as well as downstream.


To reduce noise successfully, the noise reduction component needs to be able to generate and absorb sound within the entire targeted frequency span.

Low frequencies are harder to target due to the need of powerful components. The physics behind RotoSub makes it very powerful in the demanding low frequency area. This makes the component perfect in active noise control. A small component with large noise reduction.


Without correct phase, noise suppression will not work. Noises emanating from a fan/ventilation system have a very complicated phase structure.The noise is not only generated by the fan blades but also by the interaction of the rotating flow with surrounding components.


Anti sound generated from a RotoSub-fan follows this complicated phase structure. This means that the anti sound will reduce noise all the way down the flow. It also means that RotoSub will reduce noise upstream and downstream simultaneously.


To actively reduce noise, the anti-noise source needs to be inserted in the heart of the flow. When using active noise control, position is vital.

A noise source targeted with active noise control, will have noise maxima and minima unless the noise and anti-sound can be successfully joined. The RotoSub uses the fan for anti-sound, positioning the component in the optimum position, in flow at the noise source.