I am new to silent pc building so if I am making some lame assumptions please correct me.
For example this is claimed properties of Noctua NF-S12-1200 fan.
airflow noise 1200 rpm 81 m³/h 17 dB 600 rpm 41 m³/h <6 dB
If I recall high school physics correctly two 6dB are summed as this:
10 * log ( 2 * 10^ 0.6) = 9dB
So two Noctua fans running 600rpm should make considerably less noise that one fan running 1200 rpm while airflow is unchanged.
Is this just a property of particular Noctua fans or is this a general principle?
Also how does my theoretical assumption about noise addition stand in reality? What about case resonance?