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 Post subject: A physical comparison of 4 120mm fans
PostPosted: Mon Jul 31, 2006 1:18 pm 
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Joined: Thu Dec 15, 2005 11:06 am
Posts: 2049
Location: Klamath Falls, OR
All 7-blade 1" thick 120mm fans are the same physically, right? Who could doubt it? And if they are geometrically the same, then their performance in terms of CFM and back pressure automatically becomes the same.

I decided to take a look at the three 120mm 1" thick fans I have that have the lowest motor noise, and one more fan whose motor noise is obviously higher but which other persons have described as a good, quiet performer.

Yate Loon D12SL-12 (quietest motor)
Global Win NCB
Enermax UC-12EB
Scythe S-Flex E (noisiest motor)

So I took a careful look at these fans physically. I was really surprised: the fans are obviously different! In some performance-related ways!

Scythe S-Flex E (smallest gap)
Enermax UC-12EB
Yate Loon D12SL-12
Global Win NCB (largest gap)

I'm talking about the gap between the end of the fan blade and the fan case. A small gap gives good pressure and CFM performance at low RPMs but higher "whoosh" noise at higher RPMs. There was a huge difference in the gaps on these 4 fans. The difference was almost 1, 2, 3, 4, with the GW gap close to 4 times greater than the S-Flex.

This effect alone could account for reports of poor CFM for the GW at low RPMs. Similarly, in cases with high back-pressure (or on HSs with closely spaced fins), the GW's CFM would fall off faster than the S-Flex's. On the other hand, the GW might well have the lower "whoosh" noise at higher RPMs.

This gap size was the biggest difference, but there were others:

Blade shape: The S-Flex and UC-12EB had almost identically shaped blades. The D12SL seemed to have a lower pitch - it seemed to "bite" less air per revolution. And when I placed a white sheet of paper behind each fan, there was obviously less "white" showing past the GW blades than with the other 3 fans - an indication that the average chord width of the fan blade was significantly greater on the GW.

Oh, yes: the S-Flex has open ears, the others closed.
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According to my Kill-A-Watt meter, my computer draws 84W from the socket. Here in Klamath Falls, I get good cooling most of the year with my two 120mm fans (exhaust and modded PSU) running at 800RPM. When it gets hot, I like to boost that to 1000RPM or even higher.

We just had a heat wave, which I understand didn't just hit us here at KF. I've been using my "oiled" UC-12EB for exhaust, and I could only turn the RPM up to ~970 since my Spire SP-205 fan controller only puts out 11.0V at the high end. Perhaps for this reason, the noise remained very low.

I think I'll try the S-Flex as my exhaust, also at 970RPM, and live with it a week or two. The thing is, in the past I've been comparing motor noise while ignoring the whoosh, just listening to the stand-alone fan and not the computer system.

I've also been checking the motor noise from only one direction - but I just discovered that on the D12SL, the motor noise disappears from the other direction, while on the S-Flex and UC-12EB, the motor noise is the same in both directions and the GW is half as loud the other way.

I'm no longer confident that fan motor noise and system computer noise are well correlated, even though I've got the HDD noise whipped. But system noise takes a while to fairly evaluate - you can't test 4 different fans in minutes or hours. With mass loading on the case covers and other mods, the actual system noise level is very low (84 watts helps).

Worse, I've got a $25 fan due in tomorrow that deserves an evaluation. Sigh.


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PostPosted: Mon Jul 31, 2006 1:23 pm 
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Joined: Fri Sep 16, 2005 11:06 pm
Posts: 224
Location: Switzerland
Interesting observations. Which side were the 'loons quieter from?

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PostPosted: Tue Aug 01, 2006 5:52 am 
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Joined: Thu Dec 15, 2005 11:06 am
Posts: 2049
Location: Klamath Falls, OR
The Yate Loons - and the GW NCBs - were quieter on the exhaust side.


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