The two demands we place on a case fan - to displace as much air as possible while producing the least amount of noise - are inherently mutually exclusive. In order to move more air, a fan needs to rotate faster, which produces more sound. The easiest way to make a fan more silent is to make it turn slower, but this will of course influence the amount of air it displaces.
This is where smart designers come into the picture. Case fan manufacturers try to increase the volume of displaced air by changing the design and number of the blades. We have seen a wide variety of designs: fan blades with notches like a golf ball, blades with a slant, and serrated blades. Nothing is too crazy to try. For each new attempt the manufacturer has a (vaguely) scientific foundation of why that particular design is better. In the end, it’s the performance that counts.
The same applies to the bearings used in the fans, something we've examined previously. In addition to the tried-and-proven ball bearings and sleeve bearings there are now exotic derivations such as rifle bearings, twister bearings, and so on. The goal is always the same - less noise. Again, it’s not the design but the end result that is important."