push pull whining sound

Guest2 · 19 Aug 2015 at 22:33

I have a noctua nh-u14s and bought another nf-a15 so that I could run push-pull. When both fans are connected there is a high pitch whining sound, when either the push fan or the pull fan is connected by itself there is no whining.

I then took the clips off the pull fan and carefully placed it next to the heatsink, next turned the machine on and ran realbench video encoding.

Putting the pull fan up against the heatsink created the whining sound, moving it slightly away the sound would stop.

Is there turbulance between the two fans which is creating this annoying sound? The sound does not occur at low standard rps speeds, only when at full speed (1500 rpm for the push fan and 1200 rpm for the pull)

OLDPHART · 20 Aug 2015 at 08:53

Yes there is some turbulance between the two fans which is creating this sound.

Your temps will only be 1'c or 2'c with just a single fan giving a quieter systom.

andybird123 · 20 Aug 2015 at 10:17

Yeah, push pull fans should be matched pairs, though I partly disagree with the above, push pull can give some good gains under certain circumstances

At the very least you could try running the two fans at the same speed as that will minimise differences - or control both fans until the noise goes away, but basically the 1500 one will need to be run slower than it is

Guest2 · 20 Aug 2015 at 11:01

Do you think push pull both 1200rpm would be better than just one at 1500rpm? I also read that pulling air is better than pushing it. So best to setup the single 1500rpm fan in pull and have nothing pushing?

tyler_jrb · 20 Aug 2015 at 11:13

Even identicle fans will give some turbulence and you will get the noise. Push/pull will give better temps but they do give more noise. If you slowed them down then it will quieten them down and still give better than single fan performance.

single fan vs push pull performance will depend on the system, heatsink, rad's etc. But they can be beneficial especially for large, thick and or dense radiators, heatsinks (lol

).

Glanza · 20 Aug 2015 at 11:27

Push pull benefits are usually on very thick rads i.e Monsta, anything 45 or under it's very minimal.

Brian18741 · 20 Aug 2015 at 11:35

I remember reading on MLL a couple of years ago that push pull would always net about 30% performance increase. Is this no longer the standard thinking?

Guest2 · 20 Aug 2015 at 14:02

Thanks, is it possible to limit the 1500rpm fan to 1200rpm? I guess this is what the 'low noise adapter' is for that's included with the fans

I fitted the larger rubber anti vibration pads and seems to have helped too - but still a slight high pitched noise.

Or maybe I would be better fitting the 1400mm fan in the top of my case in front of the radiator, pulling air in from outside the case. It then passes through the cooler tower and out the back and top of my case

Guest2 · 20 Aug 2015 at 20:58

Connected the low noise adapter to fan in pull then to the cpu header and the second retail push fan to the 'cpu opt' now both are at 1200rpm and the noise has stopped.

Am I just being too simple here when I ask why Noctua recommend a 1200rpm fan with the u14s that is 1500rpm?