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Which is quieter? 2 x 80mm or 1 x 120mm???

Posted: Sat Dec 06, 2003 9:22 pm
by JPS
I am planning a new case for my current rig, one that is quieter than the Antec SX630 I currently have (plus I need more space). The SX630 has been modded to accept a Panaflo L1A 120mm intake and a Panaflo M1A 92mm exhaust. It is quiet, but I think I can do better.

I am considering either of the following:

1) LX-6A19 with Panaflo or Papst 120mm intake and exhaust


2) Antec/Cheiftec 1040 with 2 x 80mm Panaflo/Papst intake and 2 x 80mm Panaflo/Papst exhaust

Also, this system will be overclocked hard, i.e. Athlon XP 1700+ at 2250MHz...

Which setup do y'all think would be the most quiet? :wink:

Posted: Sun Dec 07, 2003 12:42 am
by Winston
I believe 1x120mm will be more quiet than 2x80mm. First of all, it is the diff between 1 and 2 motors running. Secondly, a 120mm fan can move the same amount of air as an 80mm, but at a lower speed. Thirdly, the noise from a 120mm will be of a lower frequency, so it will be less annoying than the noise from an 80mm (just imagine the high-pitch noise of any 40mm fan running at high speed).

As for the choice of brand, I can't say much since I've never tried the Panaflo fans myself. I have used Papst 80mm for CPU tho, and it is very very quiet (it's the 8412N2GL, 19.5cfm, 12dB(A), 1500rpm). You will see that many others on this forums are very fond of the Panaflo's tho, and they say that they're even less noisy than the Papst's. My problem is that the place I buy my stuff from doesn't have the Panaflo's, so I've settled for Papst for now.

Hope this was of at least some help! :)

Posted: Sun Dec 07, 2003 1:30 am
by jverheul

Posted: Sun Dec 07, 2003 1:34 am
by MikeC
This question has been posed a few times before. The answer depends on the airflow you need, and on the specific fans.

If I compare 2 Panaflo 80Ls vs, at 5~7V they are quieter by a small margin than the best 120mm fan I have, a very good sample from an Antec Sonata. I have several of these Antec 120mm fans; this particular one is exceptionally quiet. There is a greater amount of lower frequency drone or hum from the 120mm fans that seems to get amplified by the air or panels a typical case; this happens much less with 80mm fans, even 2 of them.

In any case, the fundamentals of noise addition say that two 10 dBA (@1m) fans make 13 dBA. The Panaflo at 5V is somewhere around that 10 dBA level. No 120cm comes even vaguely close at 5V. On the other hand, the airflow/noise ratio of the 120mm fan probably always exceeds the 2 Panaflos, and at some point somewhere above 7V, depending on the Particular 120mm fan, it may become a better choice, not only for airflow but noise.

The gmJamez's Variation excel file of fan spec calculations (airflow and noise at reduced voltages extrapolated from the manufacturers' 12V specs) in the article Choosing Fans for Quiet, High Airflow: A Scientific Approach shows a 120mm NMB 4710NL B10 fan that is spec'd at 12V for:

59cfm * 1550rpm * 27dBA

Those numbers seem very optimistic to me, but if we take them at face value, the extrapolated 5V numbers are:

25cfm * 646rpm * 14dBA

That's certainly better cfm than you would get from two Panaflo 80Ls at 5V, and close enough in dBA to be probably indistinguishable, but until someone actually tries a few of the NMB fans, we won't know whether --

-- the acoustic signature is no more annoying,
-- the lower frequency humming will be more noticeable, and
-- whether received reality of these fans follows theporical calculations.

OFF-TOPIC: If you have not read the article Choosing Fans for Quiet, High Airflow: A Scientific Approach, it is a compelling (almost obligatory) read for those studying fans, noise & cooling.

EDIT: The gmJamez's Variation excel file is an updated, scientifically more accurate version of the original file linked in jverheul's quick response. That article has become a bit confusing; I need to tidy it up a bit for readers who never saw how it evolved, but it is definitely worth reading and studying carefully. A wealth of useful info there.

Posted: Sun Dec 07, 2003 2:03 am
by dukla2000