After watching multiple reviews about the Fractal Design R4 i have chosen to use this in my build that i hope to get,but im still not sure what fans to use. i want to add more fans so i keep it cooler, i am interested in the corsair Air series AF120 or 140 but im not sure if they will be compatible in the front fan holder.i do want to use quiet/silent fans so thats why im interested in the corsair air series.
I don't see why they wouldn't fit in the front and if they dont you can move your HDD cage.
If they are regular 120/140mm fans they should fit just fine.
Also I think the fans from fractal design are pretty quiet, I am getting my Define XL R2 sometime next week so I did check out some revieuws of fractals stock fans and they seemed to be pretty quiet.
These are the same fans that are pre-installed on the Define R4. Buy a couple of these and you'll have better airflow while still remaining silent :)