Thank you so much for explain..Most cases run 30° to 50°, depending on ambient temps, loads, airflow. Unfortunately, default for sys_fan headers is @ 40% at 30° to 100% at 70°, so fan curves start out messed up to begin with.
There's no realistic performance difference between 90% and 100%, but you'll find that last 10% fan will double the noise output.
JayZ says one thing about fans, but I disagree. He says fan types don't really matter. I believe they do.
With Noctua, F series is a force directed fan. It's blades and shroud are designed to channel air exhaust in a 90° flow. This is optimal for a rad/heatsink as all the static pressure is directed straight through the restriction. Also works well in restricted or obstructed cases for moving the air past all that.
The S series is the opposite. High rpm, high cfm fans with low static pressure. Perfect for exhausts since they move a ton of air, but once out of the case that air is irrelevant, so little static pressure is really required.
The P series is the hybrid. Less static pressure than F, less cfm than S, but higher static pressure/cfm in opposition. Some call that balanced. So it works well with some heatsinks, has a relatively shallow cone, and moves a lot of air, making it better overall for intakes.
The A series is a better version of the older P series, has higher cfm, higher static pressure, so a broader range of affect, almost as good as the F/P series in their specialty.
That theory works for All fan types. Put an S at intake, you'll move plenty of air in, but it doesn't go anywhere, just sorta drifts towards the exit, which tends to starve the gpu. Put an F at intake, the gpu gets flooded with air, but the cpu sees very little fresh air as a result, the majority of its source being warmer air exhaust from the gpu. So a hybrid with a decent cone size and enough static pressure to feed a gpu, will supply both, simultaneously, with fresh outside air.
A case has 3 zones. High pressure in the path of any intakes, zero pressure centrally, low pressure in front of any exhaust fans. The objective is to negate as much of the zero pressure as possible. Nature abhors a vacuum, so any air in the case will gravitate towards the low pressure area naturally. With a large central area, that's slow moving air, the low pressure area providing all the attraction. With a small central area, airflow is faster as low pressure suction is in addition to high pressure push.
So static/hybrids in front, cfm/hybrids in rear is optimal types. Also to consider is placement. Most times you'll want airflow in a single direction, front to back. Putting additional fans on bottom can be counter productive as that forces air away from the gpu. Putting intake on top/front with high rpm forces front intake downwards etc. But top/front intake and low rpm will add to front/top and help out cooler fans.
Which is where setting up fan curves comes into play. As Darkbreeze said, most ppl do Not set the right curves, with the right sensors. A top mounted front intake at 300rpm will help a cpu aircooler, that same fan at 1300rpm will destroy cpu temps. As will having that fan as exhaust, it'll just suck all the air from any high mounted front intake, away from the cpu fan.
Too many fans creates conflicts, not enough fans doesn't resolve issues. The trick is to use the right amount of fans, to do the job right and to have those fans setup correctly so they Can do the job right.
I adjust fans using Prime95 small fft, @ 70% workers, so on my 16thread cpu, I use just 12 workers. Simultaneously run MSI Kombuster fuzzy donut. That gives me @ most demanding game setup.
Then I give the case a solid hour to acclimate the power loads and temps. I use CoreTemp cpu/gpu and fan software to lower/raise intake/exhausts 100-200rpm stages and see how that affects noise output vs temps giving 5 mins or so between speed adjustments. I'm looking for max with compromise. Then do the same at idle, looking for minimum. Then I play my favorite game, see where that linear line puts me and then adjust the center of the curve up/down as I feel I need or can.
The end result is no matter what I play, it'll be under maximum, so under maximum noise tolerance, under max allowable temps (I don't care exactly what that number is as long as it's decent/safe, a cpu at 50° is exactly the same as at 70°) and at idle the pc is silent and not overly warm (idle of 32° isn't any different to 38°).
If I spend anything less than @ 4hrs messing with fan curves, I've either gotten real lucky with guessing the settings or gotten real lazy and not done a thorough job.