Xbitlab measurements say 120mm fans give more cfm 4 same dBA

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photonblaster
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Xbitlab measurements say 120mm fans give more cfm 4 same dBA

Post by photonblaster » Sat Jan 15, 2011 5:51 pm

Xbitlab did a huge amount of work in fan round ups, but with 31dBA noise floor measuements.
If you compare the 140mm and 120mm results on the two reviews (last fall and summer of 2009, respectively)
http://www.xbitlabs.com/articles/cooler ... html#sect0
http://www.xbitlabs.com/articles/cooler ... up_28.html
The best 140mm fans at 33 dBA gives ~15+ cfm, the best 120mm give about 23+. That's 50% more cfm at the same noise level.

Can I use these results to make a 120 vs 140 mm fan size decision for a custom case build?

I am particularily worried about the dBA being too close to the noise floor...if this changes between reviews it can greatly distort the results. The background needs to be given for each measurement (there is so much measurement time here there would have been days begtween sets of readings) but like most reviews it does not.

If a fan or two from the 120mm roundup was used while doing the 140mm round up one could be more comfortable with comparing the two reviews.

To their credit, qualitative ranking of fans is in general very close to SPCR discussions. But I did not find any usefull search results on SPCR after hours of trying to find something...information overload.

danimal
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Re: Xbitlab measurements say 120mm fans give more cfm 4 same

Post by danimal » Sat Jan 15, 2011 8:28 pm

those reviews are over a year apart, did they use the exact same measuring techniques in both? i'm guessing not, because i have a hard time believing that a 120mm fan blows that much more air, over a 140mm fan.

also, if i remember correctly, the 140mm fan review did not test static pressure(?), which probably won't concern you, since you are looking at case fans.

quest_for_silence
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Re: Xbitlab measurements say 120mm fans give more cfm 4 same

Post by quest_for_silence » Sun Jan 16, 2011 2:13 am

photonblaster wrote:Can I use these results to make a 120 vs 140 mm fan size decision for a custom case build?

If you take those results as relative ones and not absolute ones, I think it may be not actually unreasonable to do so.

Just as food for thought, if you give a look to the recent SPCR Noctua NH-C14 test, you may find that the Nexus 120mm used as single (bottom) fan have an advantage over a single (botton) Noctua 140mm fan of about 2°C on CPU temp.
At the same time you may argue that the Noctua may have a slight less noise than the Nexus at the lowest voltage with a modest temperature worsening for the CPU, but with a noticeably advantage for VRM cooling and a lesser one on NB.

There's nothing decisive, but as I don't trust Xbit-Labs noise measures I mean these numbers might you help a bit further.
Regards,
Luca

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frenchie
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Re: Xbitlab measurements say 120mm fans give more cfm 4 same

Post by frenchie » Sun Jan 16, 2011 7:23 am

Compare the testing methodology by SPCR and xbitlab M
http://www.silentpcreview.com/article734-page2.html
vs
http://www.xbitlabs.com/articles/cooler ... html#sect0
http://www.xbitlabs.com/articles/cooler ... html#sect0
quest_for_silence wrote:Just as food for thought, if you give a look to the recent SPCR Noctua NH-C14 test, you may find that the Nexus 120mm used as single (bottom) fan have an advantage over a single (botton) Noctua 140mm fan of about 2°C on CPU temp.
At the same time you may argue that the Noctua may have a slight less noise than the Nexus at the lowest voltage with a modest temperature worsening for the CPU, but with a noticeably advantage for VRM cooling and a lesser one on NB.
+1 Very good summary
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photonblaster
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Re: Xbitlab measurements say 120mm fans give more cfm 4 same

Post by photonblaster » Sun Jan 16, 2011 6:42 pm

Thanks, everyone.
I should have twigged on the methodology change at Xbitlab, I have read both links at one time or another.

To summarize what I found in the links if anyone is interested:
Xbitlab's 140mm fan review used a turbulance reducing method (an array of straws) very similar to one that SPCR evaluated and rejected as having too much pressure drop. Their 120mm fan measurement system had extremely low pressure drop, so theri two methods are not comparable. The 50% increase in CFM of 120 over 140 is due to the higher pressure drop for the 140mm tests.

But on a qualitiative basis for each group of fans, provided the background noise levels do not change too much, the results are probably usefull, and as I said in the first post, actually seem to qualitatively follow what SPCR has measured.

At least I got it right that they should have measured some 120mm fan(s) in the new setup, this would have helped identify the big changes.

BTW, remeasuring some reference units at the beginning of a new set of tests to make sure nothing has gone awry with your test system is very good practice in experimental physics and industry product measurements. Not only do you make sure the readings are still similar to previous ones, you are able to calculate your measurement repeatability. Not that I recommend doing full fledged statistical process control charts or anything like that, but just a quick validation test.

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