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 Post subject: nexus 120mm fan questionPosted: Wed Oct 12, 2005 2:06 pm

Joined: Sun Aug 14, 2005 3:21 pm
Posts: 133
Location: Belgium
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.

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 Post subject: Re: nexus 120mm fan questionPosted: Wed Oct 12, 2005 10:53 pm

Joined: Sun Mar 09, 2003 12:27 pm
Posts: 1465
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.

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2009/Oct: Jetway JNC81-LF * 4850e naked under fanless Xigmatek Apache * Antec mini Skeleton w/Nexus 120mm PWM fan * Delta 90W brick w/Skeleton DC-DC board * WD2500BEVT 250Gb blue

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 Post subject: Posted: Thu Oct 13, 2005 1:18 am

Joined: Sun Mar 20, 2005 1:18 pm
Posts: 467
Location: Umea, Sweden.
For me, the lowest setting on the fan mate (5V?) equals about 520RPM on a nexus 120mm fan.

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 Post subject: Posted: Thu Oct 13, 2005 4:48 am

Joined: Wed Sep 21, 2005 5:57 am
Posts: 174
Location: Germany
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:
V   RPM   CFM   dBA*

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

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 Post subject: Posted: Thu Oct 13, 2005 12:28 pm

Joined: Sun Mar 09, 2003 12:27 pm
Posts: 1465
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!

_________________
2009/Oct: Jetway JNC81-LF * 4850e naked under fanless Xigmatek Apache * Antec mini Skeleton w/Nexus 120mm PWM fan * Delta 90W brick w/Skeleton DC-DC board * WD2500BEVT 250Gb blue

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 Post subject: Posted: Thu Oct 13, 2005 1:22 pm

Joined: Sun Aug 14, 2005 3:21 pm
Posts: 133
Location: Belgium
thanks for the aswers! This helped me out.
Onto the next question, but will post this in another section.

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 Post subject: Posted: Fri Oct 14, 2005 1:19 am

Joined: Wed Sep 21, 2005 5:57 am
Posts: 174
Location: Germany
Thanks dukla2000!

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

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