Be very careful when improvising ideas with fans for miners. They are loud for a reason--moving HIGH amounts of air.
Changing, removing, or tampering could result in the loss of your machine or cause a major fire!
If removing the noise is what you are after, you might check out this thread for sound proofing.
https://bitcointalk.org/index.php?topic=2245487.0Be safe!
Got 2 boxes built.
R4 config is more appealing to me as a form of a home heater(ex.fan coil unit).