It's not that noise isn't an issue, Apollo 10 had a big problem with noise. A roll program (barbeque mode) that kept the sides of the ship from overheating in the sunlight kept firing the reaction jets causing a banging sound. When they tried to just turn the program off and let the craft just rotate freely, it wouldn't keep oriented well enough to keep a thing called gimbal lock from happening - so they had to turn it back on. Imagine day and night with the navagation banging away with the reaction jets every so often, jolting the crew.
As for pursuing a noise canceling fan - it just seems like reinventing the wheel. Maybe this will pay off, I don't know. It just seemed to me that a few things that have worked to quite ventilation system noise could have been tried.
-Finding a better blade airfoil
-Changing the fan size
-Finding ways to get duct velocities as low as possible
-Vibration dampening of the fan
-Dynamic balancing of the fan
-Fan tip to fan shroud clearance
-Blade durability, you wouldn't want something small to get sucked through the fan and shell a blade
-Bearings, these things are going to have to last for years of operation - probably with little or no lubrication and if they fail they can make lots of noise
-Motor/speed control, throttle the fan down when it's not needed and make sure the speed control doesn't make whining noises.
-Duct geometry, air flowing through a duct can make noise all on it's own - the quietest fan won't help. Ducting can also quiet a noisy fan. Imagine the possibilities with 3D printing, radiused
bends, double walls, light weight, interior surface finish control , integrated Helmholtz resonators (possibly even adjustable).
All this and possibly even doubling as a structural component to boot!
-Noise canceling headphones, they work - they're light weight - they'll quiet noise problems we can't even think of right now. Just make sure you bring enough batteries
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)
-Don't use an old noisy Russian ventilation system - use a newer, quieter Russian ventilation system.
Those are just some ideas to think about as well. I don't know that a completely superior approach exists for any real life endeavor, but my guess is that there might be a lot of work an time needed to get even marginal results out of a noise canceling fan. One that could go into a spacecraft. This investment of time and money costs the investigation of some other solution, some other refinement. To me, the odds of achieving substantial results with this solution seem "dodgy" at best.