How loud are these fans (6)?

Control: management of fans, temp/rpm monitoring via soft/hardware

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nzone
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How loud are these fans (6)?

Post by nzone » Thu Mar 26, 2009 8:05 am

If put 6 of NF-S12-800 fans in the case, how loud are they going to be?
Noctua rated <5dBA per fan using U.L.N.A.

CyberDog
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Post by CyberDog » Thu Mar 26, 2009 8:28 am

it goes like this. 5+3+3+3+3+3 = 20. So it should be about 20 dB. But you can get whole lot different result in real life...

nzone
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Post by nzone » Thu Mar 26, 2009 8:33 am

That's still inaudible. Planning to put them on 2x360mm radiator inside the case. Thanks.

NeilBlanchard
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Post by NeilBlanchard » Thu Mar 26, 2009 8:42 am

Hi,

The 5 dBA is a lie -- there is no way they are that quiet! I think that SPCR has tested that model Noctua, and I would go by that rating.

I'm guessing that 6 of any fan will be at least audible, and it probably would be fairly noisy.

QuietOC
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Post by QuietOC » Thu Mar 26, 2009 8:56 am

CyberDog wrote:it goes like this. 5+3+3+3+3+3 = 20. So it should be about 20 dB. But you can get whole lot different result in real life...
No, it doesn't.

It should work this way:

1 fan --> x dB
2x --> 3 + x
4x = 2x(2x) --> 3 + (3 + x) = 6 + x
8x = 2x(2x(2x)) --> 3 + (3 + (3 + x)) = 9 + x
16x = 2x(2x(2x(2x))) --> 3 + (3 + (3 + (3 + x))) = 12 + x
etc...

So 6 fans would be more like +7.5 dB not +15 dB.

If all these fans are spinning at almost the same speed, the beat effect can cause the momentary noise to be much louder.
NeilBlanchard wrote:The 5 dBA is a lie -- there is no way they are that quiet! I think that SPCR has tested that model Noctua, and I would go by that rating.
SPCR's results of 20dBA @ 12V was just above the current ambient conditions, so it is not really helpful either.
Ambient noise at the time of testing was 19 dBA.

CyberDog
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Location: Kuopio, Finland

Post by CyberDog » Thu Mar 26, 2009 10:10 am

Yep. My bad. I was too tired and in too hurry... It actually is like this. two equal noise source is +3dB. So four fans is +6 to original dB (=11dB) and 6 fans is something like +7.5dB to original (=12.5dB).

But what did the Neil said is probably true. But it is really hard to find quieter fans than those on U.L.N.A... And they are probably quite quiet on that setup. But the question is that do you need that many fans or should you use some sort of duct and less fans.

Yes that result what SPCR got is too near to ambient to be reliable. And it is measured with 12 volts. Not with lover voltages.

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