two low rpm fans vs one high rpm for cpu cooler.

Driftnick · Jul 17, 2016

I have a Hyper 212x with a Noctua NF-F12 Industrial PWM 2000rpm fan on it and I'm wondering if I change to two low rpm fan's (probably Noctua fans) what kind of cooling difference if any would there be?

also would the two low rpm fan's make less noise then one high rpm fan?

Thanks for your help.

Ecky · Jul 17, 2016

One fan pushing 30cfm and one fan pulling 30cfm still only equals 30cfm passing through the heatsink, so two quiet fans would move very little more air than a single quiet fan, and considerably less than one fast, loud fan.

Two fans make double the noise (3dba) of a single fan of the same speed, which isn't very much to the human ear, but it does add noise.

Supahos · Jul 17, 2016

Rpm isn't the number you need it's all about cfm (cubic feet per min) as in how much air it blows, but yes typically 2 fans in a push/pull arrangement can run slower and quiter than a single one can to do the same job. Make sure they are blowing the same direction

Supahos · Jul 17, 2016

Ecky you know it's not quite that simple 30 cfm being blown in doesn't all come out the other side of the sink.pulling on the other side with the same force does increase airflownacross the fins. Might only allow you to slow down 10-15% but it may be quieter to run 2 slower than one fast depends on fans

Ecky · Jul 17, 2016

You're right in that it's not that simple. I haven't actually looked at any figures on it in a long time. A quick google revealed this thread on SPCR:

http://www.silentpcreview.com/forums/viewtopic.php?t=19297

The OP's conclusion there was that two undervolted Nexus fans, when not attached to a heatsink (blowing unrestricted) pushed the same air with slightly less noise than a single fan at 12v. However, posters were quick to point out that two fans blowing in parallel is not the same as two fans in a series.

I know intuition is not nearly always right, but mine tells me that two fans in push/pull probably don't have much, if any advantage over a single slightly faster fan in terms of noise vs airflow.

Ecky · Jul 17, 2016

This thread is informative as well:

http://www.silentpcreview.com/forums/viewtopic.php?t=58565

datapappan said:
Once again one must point to how fans and air flow works.

Air flow:
pushing air through a case has to overcome the pressure drop caused by impedance. Basically pressure drop is related to air flow by the square (double flow=four times pressure)

Fan:
Fans have more or less teh reverse relation, at 0 flow it gives the most pressure, and as flow increases, pressure decreases, up to a maximum (the cfm figure you can find in specs, actually at free flow in mid air)

So, for any given setup these to curves meet at the operating point.

With two fans working in parallell, they share the flow, but still has to put in the pressure. This is done by lowering rpm until the operating point is att the same pressure, at half the flow.

Again, two fans in series (push-pull) shares the pressure, but has to give the same flow. And again, lowering rpm gives a new operating point.

It's not obvious which setup gives the lowest noise, so I agree with the above - trial and error gives the best answer. It also comes into account where the fans are placed in the case, and where the case is situated in relation to the user. (A really silent PC will sit in another room...)

/ d

EDIT: Here's my current logic:

Two fans in a push/pull config would likely each be able to run at lower RPM to push the same amount of air through the heatsink. The pitch of the noise produced by the blades would be lower, and thus less irritating. However, from my experience, many fans have a pretty-close-to-fixed amount of bearing noise, which would then be coming from two fans, rather than just one. So, two fans with very quiet bearings would likely be less irritating, if not quieter than a single of the same fan, whereas two with particularly noisy bearings (such as the fans Coolermaster generally provides) would be more irritating. Marginally.

Noctua's fans have quiet bearings, but worth spending $40+ on? Probably not.

Supahos · Jul 17, 2016

Yep that was basically what Iwas saying in less words fan quality > all else one good fan hauling ass is quieter than 2 loud fans going a bit slower, but 2 good fans slower would be nearly silent but good fans are expensive... So which came first the chicken or the egg

synphul · Jul 17, 2016

A hyper 212x is almost the same as a 212 evo. Many people have added dual fans with little improvement to cooling, the cooling fins just aren't deep/thick enough to benefit much from a push/pull arrangement. Static pressure also comes into play, fans with lower static pressure may have a higher cfm rating but the airflow will fall off much faster once it hits an obstruction.

If the nf-f12 is too loud consider lowering the fan speed either by bios or dedicated fan controller or an inline noise reduction resistor type cable to drop it to 7v. I wouldn't bother with push/pull or going to the trouble to over engineer a low budget cooler. Spending $30-$40 in fans to try and improve a $20 cooler doesn't make much sense, perhaps a better cooler would be in order.

A limited number of cooling heat pipes and cooling fins mean the fan(s) either have to be turned down for noise or up for performance. A larger cooler would not only come with decent fans, more heat pipes and cooling fins mean the fans could be run at a lower speed and have equally good or better performance than a 212x/212evo.

That's why larger coolers like the tc14pe, nh-d14, dark rock pro 3 and others manage to cool very well and remain quiet. They have good cooling capacity to begin with and the fan(s) barely have to break a sweat to cool the cpu.

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two low rpm fans vs one high rpm for cpu cooler.

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