Noctua explains active noise cancellation tech
The demo is pretty dramatic in my opinion, 4 or 5 of these fans in a system should make a big difference.
"According to Noctua, the challenge with applying active noise cancellation to fans is the fact that they generate rotating pressure fields. Noctua didn't want the position of the user to be an issue, so the cancellation wave is produced within the fan itself, matching the phase and rotation of the sound being targeted. But how? Multiple magnets and a microphone."
Check out the article and video at TechReport