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### nexus 120mm fan question

Posted: Wed Oct 12, 2005 2:06 pm
I ordered a scythe ninja, I guess I will have it the day after tommorow.
It will be mounted on a P4 3.0Ghz Prescott

I want to place a nexus 120mm on it (blowing to the exhaust fan), undervolted with a zalman fanmate 2.
I want that it runs on 7V, to be sure that it starts up, but I don't have a descent voltage meter. But I can monitor the rpm's with everest.
Am I right if I do the following calculation?
1000 rpm = 12 V
100 rpm = 1,2 V
600 rpm = 7,2 V

Can I use this linear calculation? Or am I wrong?

thanks.

### Re: nexus 120mm fan question

Posted: Wed Oct 12, 2005 10:53 pm
nina wrote:Can I use this linear calculation?
Yes.

To be precise there is a slight offset as well (y = mx + c) to account for the startup electronics in the fan which has a small effect. But considering the tolerances are pretty large and the fan wont be precisely 1000rpm at precisely 12V anyway, assuming a direct voltage/rpm link is fine.

Posted: Thu Oct 13, 2005 1:18 am
For me, the lowest setting on the fan mate (5V?) equals about 520RPM on a nexus 120mm fan.

Posted: Thu Oct 13, 2005 4:48 am
The same kind of question has been recently bugging me too, but for a different reason. (I am thinking about replacing the stock fan in my S12).

Assuming a linear relationship between volt : RPM and volt : CFM, I have figured the following. I would like to know how to figure the dBA on hand different voltages. Is there an easy way to do this?

Code: Select all

``````V	RPM	CFM	dBA*

AD1212LB-A73GL (Seasonic S12 Fan)
12,	1800,0	72,0	34,4
9,5	1425,0	57,0
7,0	1050,0	42,0
5,0	750,0	30,0

Papst 4412 F/2GL
12,	1600,0	55,0	26,0
9,5	1266,7	43,5
7,0	933,3	32,1
5,0	666,7	22,9

Papst 4412 F/2GLL
12,	1200,0	41,0	18,0
9,5	950,0	32,5
7,0	700,0	23,9
5,0	500,0	17,1

Nexus D12SL-12
12,	1000,0	37,0	22,8
9,5	791,7	29,3
7,0	583,3	21,6
5,0	416,7	15,4	``````
*manufacturers spec - only indicative

Posted: Thu Oct 13, 2005 12:28 pm
sun.moon wrote:I would like to know how to figure the dBA on hand different voltages.
The standard formula for this is
dBA2 = dBA1 - 50 * log (rpm1/rpm2)
so a 4412FGL is 7.0dBA @ 5V.

Yeah, right! The formula ignores among other things the bearing noise that may not decrease at all at lower rpm. Then again I cannot hear my 4412FGL @5V @ 1m: for quality fans the formula is arguably a fair indicator, for other fans I have had the misfortune to own (e.g. Evercool EC12025M12S) it is clear to my ears there are some assumptions behind the formula that will explain cases where it clearly is wrong!

Posted: Thu Oct 13, 2005 1:22 pm
thanks for the aswers! This helped me out.
Onto the next question, but will post this in another section.

Posted: Fri Oct 14, 2005 1:19 am
Thanks dukla2000!

In this thread I posted some results based on your formula. Might be interesting for others reading here as well.