Question Fan noise level question

[wafavex204]

I'm looking at these two fans, https://pcpartpicker.com/products/compare/HkRYcf,tcVmP6/ , and I was wondering if the noise level is compounding?

Everything I've read says 2 140mm is better than 3 120mm, but I also want it to be as quiet as possible, which the 120mm are but I can't find anything about multiple noise levels

 

[Satan-IR]

What will you use the fan for? Going on a case?

The 120 one's specs says it's 3db quieter than the 140 one at 200 higher RPM. I guess we have a winner if you're primarily concerned with noise.

Although noise level is relative and depends on system load, heat generated and the RPM at which the fans need or are set to rotate. If you set a profile where they're at full speed all the time the quieter one is better.

The 140 one moves 56 CFM of air while the 120 one does 41.51 CFM. That's almost 35 percent more air movement for a 3db margin. I'd consider that too.

At the end of the day if noise is the main concern the one making less noise is the choice. Also you plan to use them in a case? What size fan does the case take? Usually they're not interchangable in term of size.

When it comes to fans usually you can't go wrong with Noctua. This one for example is a few dollars but it makes less noise than the quieter be quiet! fan and moves 60.1 CFM at max speed.
https://pcpartpicker.com/product/zxx2FT/noctua-nf-a12x25-pwm-601-cfm-120mm-fan-nf-a12x25-pwm

 

[wafavex204]

Probaly the Lian Li O11D EVO RGB - https://lian-li.com/product/o11d-evo-rgb/ or Maybe a Hyte Y60 - https://hyte.com/store/y60?v=114 or Y70 - https://hyte.com/store/y70?v=307 , so appearance is a consideration. All of them say 140mm or 120mm can be used.

 

[Paperdoc]

Look at it this way. For MAXIUM air flow at max speed and noise, with the 120's you get 3 x 41.5 = 124.5 CFM at 1700 RPM generating 20.6 dB noise PER Fan. with 140's you get 2 x 56 = 112 CFM at 1500 RPM generating 23.3 dB PER FAN again.

Now, what an automatic fan speed control does in fact is TEMPERATURE control - in this case, of the temperature as measured by a sensor on the mobo. It manipulates fan speed to achieve a TEMPERATURE target at that sensor. So if we compare those two fan set options, for any measured temperature the controls will slow down all the fans to whatever it takes to reach the target, and generally this will be to a speed that is a % of max speed. IF given the SAME % max speed signal, the 120's always will be going slightly faster than the 140"s. BUT they also will push MORE cooling air that way. So in fact the automatic system will see the temp getting lower, and let the 120's slow down more until the air flow rate they generate is very similar to what the 140's would do. BUT for SAME air flow, the pair of 140's would have to run at a higher % of Full setting. So their noise generated will be closer to their max noise figure.

There really is NO way to predict with math the actual speeds and noise generation for these fans base solely on their published specs. We can only make a qualitative guess. My guess is that, in actual use at less than full workload and max heat generations, the three 120's may be slightly quieter than a pair of 140's because the trio will run slower. That is my GUESS. I also expect that the difference in noise will be small.

Between these two options there is one other difference that MAY be significant for you. IF you expect to be running very high workloads and need maximum air flow for cooling, at top speeds the three 120's can move more air than two 140's. For workloads medium-high and less, either system will do a good job of cooling.

 

[geofelt]

I like the 140mm fans better, They move more air quietly than 120mm fans.
Noise is somewhat proportional to the RPM at which the fan needs to move.
In the above case, that is 1700 rpm which is loud vs. 1500 rpm which is
noisy. You may not need max cooling. If you can set the rpm to 1000 or less, you may not notice the fan noise.

Then, also, there are secondary considerations which can make a difference.
Vibration and tonal quality.

 

[wafavex204]

Look at it this way. For MAXIUM air flow at max speed and noise, with the 120's you get 3 x 41.5 = 124.5 CFM at 1700 RPM generating 20.6 dB noise PER Fan. with 140's you get 2 x 56 = 112 CFM at 1500 RPM generating 23.3 dB PER FAN again.

Now, what an automatic fan speed control does in fact is TEMPERATURE control - in this case, of the temperature as measured by a sensor on the mobo. It manipulates fan speed to achieve a TEMPERATURE target at that sensor. So if we compare those two fan set options, for any measured temperature the controls will slow down all the fans to whatever it takes to reach the target, and generally this will be to a speed that is a % of max speed. IF given the SAME % max speed signal, the 120's always will be going slightly faster than the 140"s. BUT they also will push MORE cooling air that way. So in fact the automatic system will see the temp getting lower, and let the 120's slow down more until the air flow rate they generate is very similar to what the 140's would do. BUT for SAME air flow, the pair of 140's would have to run at a higher % of Full setting. So their noise generated will be closer to their max noise figure.

There really is NO way to predict with math the actual speeds and noise generation for these fans base solely on their published specs. We can only make a qualitative guess. My guess is that, in actual use at less than full workload and max heat generations, the three 120's may be slightly quieter than a pair of 140's because the trio will run slower. That is my GUESS. I also expect that the difference in noise will be small.

Between these two options there is one other difference that MAY be significant for you. IF you expect to be running very high workloads and need maximum air flow for cooling, at top speeds the three 120's can move more air than two 140's. For workloads medium-high and less, either system will do a good job of cooling.

That is very detailed and informative, thank you.

 

[wafavex204]

I like the 140mm fans better, They move more air quietly than 120mm fans.
Noise is somewhat proportional to the RPM at which the fan needs to move.
In the above case, that is 1700 rpm which is loud vs. 1500 rpm which is
noisy. You may not need max cooling. If you can set the rpm to 1000 or less, you may not notice the fan noise.

Then, also, there are secondary considerations which can make a difference.
Vibration and tonal quality.

Vibration shouldn't be an issue, as far as I know there are multiple solutions for that, but tonal quality, as far as I know, isn't really something that is reviewed so I'll just have to try and see.