> There is no need to spend extra for 140. A quality 120 is negligibly higher CFM then a quality 140 at the same RPM.
Where do you get these numbers from?
Take Noctua fans for example, which are arguably some of the best on the market. A 140mm NF-A14 PWM [1] does have a throughput of 140.2 m³/h at 1,500 RPM, while a 120mm NF-A12x25 PWM [2]does only have a throughput of 84.5 m³/h at 1,700 RPM. And that even with the NF-A12x25 PWM being a newer generation fan than the NF-A14 PWM!
Thanks for that, I'm apparently just wrong. I should point out that the 140mm doesn't get the extra airflow for free, as it's about 2dB louder. The lower frequency makes up for that though, and you will probably see more than a 2dB rise in noise for adding a second 120mm fan so it is still a net win at any given CFM.
Some review says that A12x25 + 14cm adapter is superior than A14 for silent setup. I can confirm that since I have both A12x25 and A14. A12x25 is impressive but a bit disappointed for A14's bass noise. dBA isn't a perfect metric how human feel the sound annoying
I agree, but I'm confident Noctua will tackle that with the next iteration of their 140mm fans which is currently scheduled to be released in Q1 2022 [1].
The pitch is largely related to the speed at which the fan is rotating. Louder is just not true, looking at the Noctua examples that your sibling comment posted, for the 140 and 120 in the same marketing range, the 140 is louder.
I would bet you that if you operated both fans in an perfectly empty, very quiet room with a human standing next to them, one at a time, the human-perceived level of noise annoyance from the 140 would be much less due to its lower pitch.
Additionally if you use a variable fan controller to reduce the rpm on the 140 to a point where its cfm or cubic meters/hour of airflow is exactly equal to the 120, or 5-10% greater than the 120 at its default rpm, not only will its pitch be lower, but its objectively measured loudness on a decibel meter will also be less.
It used to be that bigger is better, but there are diminishing returns, and manufacturers have started making quiet fans in all sizes
[Edit]
To be clear, if the case you like happens to have 140mm fan bays, that's fine, but no need to specifically look for that.