Fan controller necessary?

[livePieck]

I am creating a new build with an NZXT S340, and I plan on buying two more Cooler Master Blade Master 120mm fans to get positive pressures.
I was wondering if I should buy an extra fan controller for these extra fans.
If it helps, my motherboard is a MSI SLI PLUS Z270.

 

[Sedivy]

No. I have the same board and you have 4 chassis fan headers plus 2 for cpu. That should be more than enough to cover all the fans in NZXT S340. You can control these fans directly from the motherboard either in bios or using command centre (utility for the mobo that can sit in your sys tray). Decide whether you're getting DC or PWM fans. Both are good though I find pwm a bit more responsive personally.
Fair warning that case isn't going to be best for your cooling. All the cases that have covers on the front have restricted airflow. I only mention it because it's a popular case and people get it and then realize this after a while. If you plan to overclock, aim for something more airflow friendly.

 

[photonboy]

I would buy 140mm fans.
Your motherboard supports both 120mm and 140mm for every slot except the top-REAR slot which supports only 120mm (you got TWO of those with the case anyway I believe).

I'm no expert, but I believe the front fans need to be more powerful (or the same and spin higher) due to the pressure loss due to internal resistance. Conversely, the EXHAUST fans don't need to be as powerful since they simply exhaust the air.

Since 140mm fans will be QUIETER (of the same type of fan) I'd go with them, not 120mm.

I've found that more than 800RPM for reasonable quality case fans is rapidly diminishing returns for cooling. Keep in mind fan control starts at 40% max RPM so be careful buying the fan.

I suggest a maximum of 1800RPM if buying a variable fan. For non-variable I'd stick with 800RPM or 1000RPM.

OTHER:
I've done EXTENSIVE testing with my intake and exhaust fans. I recommend you base fan speed in the fan software on the closest sensors to the fans you're using. In my testing I found that even though I did that my fans would never go above 800RPM. I did experiment with linking the case fans to the CPU but what happened was the CPU fan would spin up, but the case fans would not.

(I set the ramp up to start at 50degC. No point going below. Even that isn't very hot for motherboard chips.)

 

[livePieck]

I would buy 140mm fans.
Your motherboard supports both 120mm and 140mm for every slot except the top-REAR slot which supports only 120mm (you got TWO of those with the case anyway I believe).

I'm no expert, but I believe the front fans need to be more powerful (or the same and spin higher) due to the pressure loss due to internal resistance. Conversely, the EXHAUST fans don't need to be as powerful since they simply exhaust the air.

Since 140mm fans will be QUIETER (of the same type of fan) I'd go with them, not 120mm.

I've found that more than 800RPM for reasonable quality case fans is rapidly diminishing returns for cooling. Keep in mind fan control starts at 40% max RPM so be careful buying the fan.

I suggest a maximum of 1800RPM if buying a variable fan. For non-variable I'd stick with 800RPM or 1000RPM.

OTHER:
I've done EXTENSIVE testing with my intake and exhaust fans. I recommend you base fan speed in the fan software on the closest sensors to the fans you're using. In my testing I found that even though I did that my fans would never go above 800RPM. I did experiment with linking the case fans to the CPU but what happened was the CPU fan would spin up, but the case fans would not.

(I set the ramp up to start at 50degC. No point going below. Even that isn't very hot for motherboard chips.)

Do two BitFenix BFF-SCF-14025KK-RP's sound good?

 

[Sedivy]

Always check youtube for videos that show noise of the fan. Like this:
https://www.youtube.com/watch?v=LXGgqXFk5Sg
Granted, that is a bit closer than your ear will be, but it does show you range of voltages and what it sounds like on each. Find fan which you can live with noise wise.