1x120mm vs 2x92mm

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rellaghs
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1x120mm vs 2x92mm

Post by rellaghs » Thu Jun 04, 2009 8:50 am

What do you think will blow more air at the same rpm, 1x120mm or 2x92mm?
I'm thinking of changing my intake 2x92mm noctuas for 1x120mm noctua with some adapting and cutting.

RaptorX
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Post by RaptorX » Thu Jun 04, 2009 12:21 pm

I think 2 x92mm will blow more air than 1 x 120mm but the difference is very small. If used for front intake the 2x92mm solution is better because the air flow is spread more evenly across the HDD section.

dhanson865
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Post by dhanson865 » Thu Jun 04, 2009 1:37 pm

I have a solo with 2 x 92mm intake. If it came from the factory with a single 120mm intake mount instead I would have prefered it but I'm not willing to cut/mod to get that now. I just run two 92mm fans at 5v to get a similar effect.

The reason I'd rather have 1 120mm vs two 92mm is not because there is some magic or even scientific advantage in airflow or noise. The advantage is cost and choice of fans.

I can buy two 92mm fans $5 each for $10 total or I can buy one 120mm fan for $5 or $8. I can make either choice of fans sound about as quiet by lowering the voltage on the smaller fans but it would be cheaper and easier to just get the fan I want at 120mm and not have to deal with changing the voltage.

Oh and since most aftermarket heatsinks and exhaust fan mount points are 120mm it would mean I can swap fans around at will without having to keep multiple fan sizes in stock.

I really wish they'd just make the solo wider or with one less fan or whatever they think is best to give me 120mm fan mount(s) on the front instead of 92mm but even as is I'll deal with it.
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NeilBlanchard
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Post by NeilBlanchard » Thu Jun 04, 2009 3:28 pm

Hi,

If you do the math, a 120mm fan has a swept blade area of ~9503 sq mm, and two 92mm fans have a total area of ~10562 sq mm but that doesn't take into account the motor hubs. So, subtract 490 sq mm from the 120mm and 980 from the pair of 92mm, and they get closer: 9023 vs 9582 -- pretty darn close by that measure.

I think it comes down to how they are used -- the front intake in the Solo for example, if you have three or four hard drives, then the pair of 92mm has an advantage of distribution.

However, two fans spinning at the same speed always make more noise than one (even a larger) fan. Two noise sources "sum" up to some extent, and even if each is similar to the one larger fan. Also, a larger fan can move the same air at lower RPM's.
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Olle P
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Post by Olle P » Fri Jun 05, 2009 4:40 am

A single large fan is also usually more powerful (will push/pull more air against a pressure gradient).

Cheers
Olle

DrCR
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Post by DrCR » Mon Jun 22, 2009 6:04 pm

As everyone else has stated, it depends. Here's the louder 2x92mm option I'm using to cool 5 HDDs in my Linux raid-5 NAS. 1-disconnected spare (would have gone raid-6 or raid-5 + spare this time around), 1 - OS drive, 3 - Linux software raid-5).

Image

A 120mm, should I have chosen to make one fit, would not have been able to provide airflow across all the drives. Oh, and I do like foam, lots of it. :mrgreen: But the hardware and fan choice and configuration are more important.

DrCR

echn111
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Re: 1x120mm vs 2x92mm

Post by echn111 » Tue Jun 23, 2009 12:19 am

rellaghs wrote:What do you think will blow more air at the same rpm, 1x120mm or 2x92mm?
Going to adjust your question a bit to give you a straight answer.

At the same level of noise, the 1x120mm will give you more airflow than 2x92mm.

This is why everyone prefers 120mm over 92mm's if they're trying to keep noise down.

LodeHacker
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Post by LodeHacker » Tue Jun 23, 2009 12:28 am

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pyn
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Post by pyn » Fri Jul 03, 2009 4:02 pm

NeilBlanchard wrote:Hi,

If you do the math, a 120mm fan has a swept blade area of ~9503 sq mm, and two 92mm fans have a total area of ~10562 sq mm but that doesn't take into account the motor hubs. So, subtract 490 sq mm from the 120mm and 980 from the pair of 92mm, and they get closer: 9023 vs 9582 -- pretty darn close by that measure.

I think it comes down to how they are used -- the front intake in the Solo for example, if you have three or four hard drives, then the pair of 92mm has an advantage of distribution.

However, two fans spinning at the same speed always make more noise than one (even a larger) fan. Two noise sources "sum" up to some extent, and even if each is similar to the one larger fan. Also, a larger fan can move the same air at lower RPM's.
so would 2x Nexus DF1209SL-3's move roughly as much air as a Scythe S-FLEX SFF21F?

Edit: never mind, I just realized how stupid this question is. what I'm trying to figure out is if case cooling is affected by slightly negative or positive case pressure. does anyone have any input?

DrCR
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Post by DrCR » Mon Jul 20, 2009 5:21 pm

pyn wrote: is if case cooling is affected by slightly negative or positive case pressure.
Only if you have a very dusty environment (thinking of Bluefront) does it matter, and you would want a positive pressure case with a good filter. Otherwise, it's not an issue.

I personally go with a negative pressure case as it tends to be quieter having all fans in the back of the case than any in the front, closer to me. But in some cases (no pun intended) I'll make an exception for a radiator/heatercore or an array of HDDs in the front that I want to keep cool.

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