Hello again friends,

this is a tricky topic I wasn't able to find clear answer for, since most PC forums fail to understand basic concepts of decibel scale, human-perceived loudness etc...

let's assume facts first:
1) bigger fan gives more airflow than smaller fan, at same rpm (rotations per minute)
2) higher fan speed results in higher noise (due to more airflow)
3) smaller fans produce higher-pitched noise
4) more fans create slight air turbulences, always resulting in more noise compared to one fan, at same rpm
5) optimal computer case airflow is when intake and exhaust airflow is roughly same, or slighty higher intake for retaining air pressure inside case

now the doubtful thing I can't get my head around:
two fans running at lower rpm, will produce less noise than one (equally-sized) fan running at higher rpm - yes or no ??

you will most likely answer, it depends on their speeds, so my second question is:
if all those fans will have same physical size and specs, what is the rpm "ratio" to get equal airflow of one fan when using two fans spinning slower, AND, how much noise difference there will be, given the same total airflow ??

thanks for read and advice, experiences and insights

 

Yes

This one is harder.
Tough I don't think you need to be so precise. Unless two fans are very close like, say, on both sides of the CPU heatsink. But that's not what you're asking.

 

here's what I'm thinking about:
I have Fractal Design Define R5 case, equipped with 14cm exhaust and two 14cm intakes, those all fans are rather average non-PWM Fractal, so I prefer having them completely off through ASUS FanXpert BIOS, unless cpu loads heavily (CPU is cooler by Noctua NH-U14S which can do the cooling on its own most of the time)
but I'm thinking about upgrading to 14cm Noctua fans with proper (eventually also lower) idle speeds and speed curve, so I wonder if two new intake fans would be meaningful in any way compared to just one intake fan

 

I have a Define R6, with a 280mm rad (fans in pull config) on the front intake, and a single 140mm exhaust on the back (the top is closed).

I switched the front fans out for Corsair ML140s which made a decent difference. Obvs air turbulence through a rad will always make a bit of noise, but the ML fans are really quiet, and I run them at 420rpm. Even when working all day in heavy Cubase projects, the highest they'll get up to is maybe about 540-600.

The ML fans are cool - the 'ML' stands for Magnetic Levitation: basically they don't have a traditional bearing - the fan literally floats in a magnetic field, so there's no friction, the only noise you hear is the fan blades moving through the air, which is basically like quiet white noise - there's no hum or whine.

The loudest thing in my case is the Fractal exhaust fan, which I'll prob switch out for an ML at some point.

 

My last tower is a Lancool 215 with two 200mm front fans + total MESH

You can take any good tower, put 3 * 120mm fans at low speed and get ALMOST the same result.
I said ALMOST because from my experience, INDIVIDUAL small fans stacked create MORE noise than bigger slower fan.

Remember the rule : double the source, you get 3dB
1->2 fans : +3dB
1->4 fans : +6dB

Even if you lower rotation speed, you stack a LOWER freq noise and UNDER PERFORMING fans.
Fans are optimized for a certain speed.

Read this for more details (noise normalized air flow) :
https://www.gamersnexus.net/guides/3477-case-fan-standardization-tests-noise-normalized-thermals

 

Come on, Man! Jimi Hendrix had no coolers nor did he have a flame retardant guitar.

 

sweet case you got there!
anyway, on the topic, here's some comparison example from Noctua site which makes me confused:
14cm 1500rpm = 24,6 dB/A and 140,2 m3/h
14cm 1200rpm = 19,2 dB/A and 115,5 m3/h
14cm 800rpm = 11,9 dB/A and 79,8 m3/h
14cm 650rpm = 9,1 dB/A and 66,4 m3/h

so by your "doubling rule +3dB" I would get about twice less noise (14,9 compared to 24,6) while slightly higher airflow by using two 800rpm fans compared to one 1500rpm fan
??

 

If it's any good, I have Fractal Design R6 with one Noctua NF-A14 ULN on the front and another one in the back to pull air out. Noctua NH-U12A CPU cooler for Intel i9-9900k. Dead quiet and cool under heaviest tasks.

 

Generally bigger fans will move more air. However, airflow is related to the cubic feet per minute (CFM) rating on the fan. In other words, bigger is not 100 % better all the time. Also, when it comes to airflow per se, we cannot overlook that the layout of your case and how all components and cables are positioned will come into play. Sometimes a smaller fan will do a better job.

 

Totally agree. I've learned that the hard way
All in all - good case, proper cable management and airflow inside the case is very important. Like I said in previous post, just 2 fans can do great job if placed properly.

 

hmm then I wonder if second fan in front would make any worthy difference, eventually even less noise?

 

Well, I have another Fractal Design fan in front just sitting there. On one occasion I've switched it on and got a bit more noise and just 1-2 degrees lower temp. So I turned it off again.

 

right my pc has about 10 or so fans 3 at the front 3 in push the at the top in pull 6 on my radiator in push pull (where fans on the bottom of the radiator pull air in and the fans on top of my radiator push air out ) 2 on the side panel of my case one 12 mm one 14 mm 12 mm in pull 14 in push 2 fans on my gpu and 2 cpu block in push (so it draws air from the radiator fans ) 3 back fans at the case 2 that draws heat away frommy pc so pull and one faceing outward so it can draw cool air into the case from the back. acutically i have set them all manually in the bios. You want them to be set in a way that your pc stays cool underload aswell as acutically to your likeing its all trial and error.
I personally have my push fans higher in terms of rpm higher than the push fans because you want there to be cool air drawn in to the pc and hot air to be released. Also most gpu software now (i know msi does so does asus ) lets you create fan curves not just for your gpu but system fans aswell just set yourself a curve in that to your likeing. AQll my fans have different rpms because of the way there configured.

 

Last edited: Jan 25, 2021

Fans arent just about acoustics in the end tho, if you run several HDDs you should have the intake fan blowing on them.

The type of fan and brand of fan dont matter as much as having PWM fans that can spin down to very slow and let the temp sensors regulate them

 

Errr yes? hehehe... It depends how much lower the 2 fans are spinning. As a rule of thumb, @Pipotron3000 gave the correct answer when it comes to db rated when adding more fans at the same speed. Thing is how low can your fans spin and how much noise vs how much air they produce when spinning at very low speeds which i will adress with a simple example next.

It heavily depends on the fan's efficiency. Some fans (ie. Noctua) are more efficient than others in low rpms. Changing a decent case's fans for Noctuas makes a lot of sense if you find that your fans are noisy even at their lowest rpm setting possible. And when i say decent case, i mean a case that has an open front grill or mesh that allows a proper amount of air to be sucked in.
With Noctua NF-S12A 120 or 140 mm fans as my primary example, you can have 2 or 3 fans as intakes and one exhaust spinning at ~500-600 rpms with adequate airflow and this practically makes your pc very quiet at ~24-25 db (inside the case), if the rest of the cooling components are of equivalent quality. These don't come cheap of course, you might find that 4 of these Noctuas cost more than your brand new pc case lol. The cheaper option from Noctua is the NF-S12B-Redux which is less efficient but still great at around 18db (for 1 fan, about 27-28db for 4 which is still great).
I could go on for hours on these and make reference to a great number of brands with good and great fans but it's kinda pointless i guess because there is a ton of bibliography and reviews/tests on (case) fans in the web. What the DIY users have to always avoid, is creating negative static air pressure within the case which will ruin airflow no matter how good or many fans you have.
Cheers

 

Last edited: Jan 26, 2021

no, I basically finished my transition to SSD-only setup,
HDDs are only in my NAS

 

if you'd ask me few years back, I'd be tempted to make a similar setup,
but right now, I have all case fans off, only cpu air cooler fan running at 880rpm, cpu temp being 55°C and gpu 54°C (gpu fans not spinning either) while running my hackintosh and another VM in Parallels, cpu dynamically boosting between 1.2 to 4.3GHz, I mean, more fans don't magically drop temps far close to ambient room temp, so I don't think I'd ever be considering this many fans you mention

 

I have the same case as you tzzsmk(Fractal Devine R5), and hope you don't mind if I ask a question about fan voltage & placement here, in your thread?!

I think I start with the fan brand, which are ARCTIC F12 PWM PST Value Pack(5 Fans)*.
Stock fans get obviously replaced by that pack!
The fans have this daisy-chain tech for up to 4 fans in series, and I ask my self, if the voltage will drop to a point that those fans will not spin anymore to their full potential, if I use it?
I don't want to put 4 fans on one header, but maybe 2, to get a cleaner cable management...!

Another question I have is, if the placement of 2 additional fans on the bottom as intake fans makes sense**?
My CPU cooler(ARCTIC Liquid Freezer II 240)sits on the top, and pushes the air out of the case.
All, but one HDD-cage on top are removed for better airflow.
The case sits on a trolley 10 - 15 cm above the floor.


ARCTIC F12 PWM PST
*https://www.amazon.com/-/de/dp/B00NTUJTAK/ref=sr_1_1?__mk_de_DE=ÅMÅŽÕÑ&crid=1TXRZINGOPMZE&dchild=1&keywords=arctic+f12+pwm+pst+-+value+pack+5+pc&qid=1611615781&sprefix=ARCTIC+F12+PWM+PST+,aps,287&sr=8-1


**To get a better picture about the inside of the case
https://www.fractal-design.com/wp-content/uploads/2019/06/Define-R5-Black_12-2.jpg

 

Last edited: Jan 26, 2021

I know, maybe this is a kind of a not that informative answer but this is what helped me.
1. Try to keep your PC, out of the control room. This is the best way to avoid computer noise but then the cost of cables will increase and if you are using Thunderbolt cables and HDMI 2.1 cables, the cost of cables will increase substantially.
2. What I did was, I created a 4 walled box. Kind of like a straight, rectangular Tube (so out of 6 sides, 2 sides are open). Now Place the PC inside the Box. The length of the box is roughly 4 times the length of the PC case. Now, put insulation materials on the inside walls of the box. This can reduce some Noise coming out of the PC.
Now, fans make mostly Low mid, High mid and High frequency.
Highs are directional, high mids are fairly directional.
So, what I did was, this tubular box, is perpendicular to the line joining the mid point of two speakers and myself.
I was sble to redue pc noise a lot.
Also, on the open sides, we can make hinged doors that stay at 45° and 45° angle respectively.

You can see the box design here.
This is what looks from the front wall of your studio.
You're on the opposite side of this box.
This will not hamper windflow.
I have tested this design with Threadripper 1950X with Enermax liqtech 360 TR4 cooler and around 80-95% load and the airflow was right and the temperature remained as usual compared to the situation without the box.

This may look like off topic but this particular design helped.

Now
CONS:
You will not be able to show off your beautiful, Plex Glass body PC Case or All aluminum PC case, your RGB lightings in side PC, your cool Vertical GPU etc.

Now, atm, due to some rebuilding work going on, I cannot post the full pictures.
But I may post the actual pictures with the data of the noise and all later in April I believe.

 

Last edited: Jan 26, 2021

@taskforce nailed it : RPM efficiency is the key to those "fan stacking"
It is NOT linear

Read the article i posted and you will see a single 140 front and single 120 back is ENOUGH with a good case.
It will create positive pressure and solve most troubles. Even at mid power.
Yes, TWO fans.

And i would even say a SINGLE good large front PWM can be enough for most ppl.
With a mesh front, good cable management.

Problems start with those "damped" cases with obstructed front panel.
You think they are more silent ... but you need TWICE fans to get enough pressure.
Back to square one :D