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Fans v. noise/flow

D

Doubl3KiLL

2[H]4U
Joined
Nov 13, 2002
Messages
2,759
So, I've got an upcoming build making it way closer and closer, so you all are probably going to see a lot of threads from me as Ive kind of lost touch with this kind of thing:D Im getting everything lined up now because it must be perfect. My question is this: I've spent about anh our tonight looking through fans, but there rated noise levels and CFM just seem so out there. Are they to be trusted? I see this one, that on paper looks great, 69CFM with a 19 db-A rating, but that just seems rediculous when similar looking fans have a 25 db rating to 41CFM.

What constitues as loud anyway? is 25db-A loud? by loud I mean obvious there is a fan running somewhere in the room.

What im looking for is really the highest CFM to the lowest DB obviously. the 69 to 19 one would be stellar if its true. The one im looking at is this one btw. Id probably end up pulling the LEDs, Id prefer to not have the lights, but on paper its a great fan, but how do these really end up?...

EDIT: These Noctua fans look like they are a solid choice. Seemingly silent with good flow.
 
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As soon as I saw the specs you gave I already knew you were talking about the CM fans, and no, they can not be trusted. All the numbers are fluff, even look at the specs, it says "Up to 69CFM (maximum RPM)" notice the at maximum RPM part, wile the noise rating is from the slowest speed (which I believe is 700rpm). If you want some info on fans, go to SPCR, read the reviews. For noise ratings that might be close, I would only put some faith in Delta, NMB/Panaflo and other OEM fan mfg's. right now the choice is with Scythe, they have some great fans at awesome prices for the performance, wile Noctua is good, they are much more than Scythe fans and don't perform any better. For non-horizontal mounted case fans the choice is Slipstreams (most people go with the 1,200rpm model) and for a HS or rad it's the GT fan.
 
Thanks for the links, I'm reading up on those now. I still like the Noctua's, as they still push very convincing numbers, and a few reviews Ive read of them (im actually interested in the NF-P12 model, not the one reviewed at SPCR) having nothing but excellent things to say. The Nexus ones seem like a solid choice as well, and the black/white would be alot more feng shui with my hardware/design.

I guess my only remaining question is, in a real life senario what is high and what is low? from reading these things it seems like ~20 is the barely audible range, in which I would like to be. is ~55CFM a mediocre range? would a rating of ~55cfm be fantastic for a ~20db-A rating?

Id like to sacrifice as little performance as possible while keeping things quite.
 
Sure, Noctua are good fans, but as I said, much more cost than Scythe, it's not important that SPCR review the fan you are looking at, the point is to see how far the numbers differ from the stated mfg's claims. Like for the fan they tested, the mfg claims 48CFM@17dBA wile the test shows they only push 38CFM@25dBA that's a whopping 8dBA and 10CFM they are off. And yes, Scythe is the same way. What I am saying is look at the numbers from SPCR's reviews and don't go by what the mfg's claim, the Scythe fans are going to be just as good if not better than the Noctua's in CFM to dBA wile being a good deal cheaper, IF you still want to pay more for the Noctua's, go right ahead, just don't pick them because they have better "fluff" numbers.

Also, you are NOT going to find a fan that pushes 50CFM+ at ~20dBA, even if the fan was 100% silent, I mean SILENT, the air it self coming out of the fan would make more noise than that. Best you might get right now is 30CFM@20dBA (which is more than enough to cool most computers), keep in mind that the average library is 30dBA. Also, the dBA rating is logarithmic and not linear, and for every 10dBA increase you have a doubling of perceived sound level.
 
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Excellent, you have supplied me with exactly the information I came here for. I think I have enough now to base my decision, thanks BlueFireIce.
 
BlueFireIce said:
Also, the dBA rating is logarithmic and not linear, and for every 10dBA increase you have a doubling of perceived sound level.
Click to expand...

I think you mean for every 3 dBA increase, you get a doubling of perceived sound level. :)
 
No, BlueFireIce is correct.

When you combine the sound of 2 exact fans, it raises 3dB. (30db+30db = 33dB)

It takes double the wattage or power to increase 6dB.
It takes a 9-11dB increase to sound 2x as loud via human perception of loudness.
"The perceived loudness is NOT proportional to the intensity of the sound."

http://www.newton.dep.anl.gov/askasci/eng99/eng99325.htm
 
My current favorites are Enermax Magma 12cm fans - but buy them only if you have a really good fan controller, as their best voltage/noise ratio is between 500 and 1000RPM which means ~4-7V. And especially the lower side of that is a problem for most fan controllers. They are beasts at full speed, but silent ones at low voltages, yet they still push a lot of air.
 
djgizmo said:
No, BlueFireIce is correct.

When you combine the sound of 2 exact fans, it raises 3dB. (30db+30db = 33dB)

It takes double the wattage or power to increase 6dB.
It takes a 9-11dB increase to sound 2x as loud via human perception of loudness.
"The perceived loudness is NOT proportional to the intensity of the sound."

http://www.newton.dep.anl.gov/askasci/eng99/eng99325.htm
Click to expand...

Correct. Which is why in some cases it is better to add more fans than to get a single more powerful fan.

To x509, I believe you are thinking about the acoustic power or sound intensity (energy quantity), which doubles every 3dB.
 
I'm not a big fan of the Slipstreams. Of the five that I bought, I've had three replaced by Scythe (due to motor grinding) with upgrades to S-Flex's, one was gutted to make a shroud because that had severe motor grind as well, and only one is still working which is mounted to only blow cool air towards my video card.

Personally, I would go with the S-Flex's. They seem to be higher quality fans overall, albeit not as quiet as the Slipstreams (especially considering that I have the S-Flex G line), but for sure stronger when it comes to static pressure and more versatile in terms of mounting positions (can be mounted horizontally or vertically). However, once you hook them up to a fan controller, you can customize how loud or quiet you want the fans to be. Granted they're not exactly cheap either, but definitely nowhere near as expensive as Noctua's and well worth the price considering their performance. If you buy in quantity from places like Sidewinder Computer, they even offer you a slight discount so the cost per fan works out better.

If you don't want to spend that much on fans though, the next best thing, in my opinion, would be the Yate Loons from Petra's Tech Shop. These fans are also very good in terms of noise profile and static pressure. However, it is not advisable to mount these fans in the horizontal position as it tends to wear out the bearings prematurely. On the other hand, your experience may be different as I've seen them used on watercooling radiators in that orientation without problems. Plus they're so cheap that they can be virtually replaced without much of any problems.
 
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