was posted 3 days ago in /c/Technology, here :
https://lemmy.world/post/15468260
what they did :

"Our product takes in a full blow of air and separates it," said team member Leen Alfaoury. "Some of that air comes out as it is, and part of it comes out shifted. The combination of these two sections of the air makes the blower less noisy."

... "It ultimately dampens the sound as it leaves, but it keeps all that force, which is the beauty of it."

Their design cuts the most shrill and annoying frequencies by about 12 decibels, which all but removes them, making them 94% quieter.