Found: the world's quietest production 120mm fan

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Felger Carbon
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Found: the world's quietest production 120mm fan

Post by Felger Carbon » Sat Jun 30, 2007 10:46 am

This is not a joke.

We're talking about standard 7-blade 120mm x 25mm fans, normal pitch, widely available for purchase. That means you can see for yourself.

I was looking among the usual suspects - Yate Loon, GW NCB, S-Flex, fans like that. I was looking for fans with low bearing noise, whose bearing noise scaled down as the RPM dropped. This latter point requires holding the fan closer and closer to your ear to confirm there's no discontinuity in bearing noise.

Among the fans that met the above criteria, the champion would be the one that turned the lowest RPM, yet kept on running.

Obvious fans to test include 800RPM fans such as the Evercool EGF and the S-Flex D. The latter won't run at 5V (I'm talking running, not starting), and the EGF runs at 6V but not 4V and I didn't try to pin it down closer than that.

The GW NCB was a prime candidate. I used my newish Extech stroboscope for measuring RPM and a 4-1/2 digit dmm to measure the voltage. Why voltage? To keep the stroboscope numbers honest. A fan turning 1000RPM will also "strobe" at 500RPM and 333.3RPM and 250RPM... you get the idea.

I selected one of my NCBs at random, and here's what I got: 12V 1289, 8V 971, 6V 746, 4V 491, 3.5V 405, 3V 319, and 2.8V 141RPM. If you plot that, you'll see that the fan motor controller IC goes to hell below 3V, but is still hanging by its fingernails - barely - at 2.8V. I think I'd be comfortable running the NCB at 3V, which is 319RPM.

All the quiet 120mm fans that can run at 1000RPM measure about the same dBA at that RPM. A fan running 319RPM is 29.77dBA quieter than at 1000RPM by the 60*LOG10(rpm1/rpm2) rule. So does that make the NCB our quiet-fan champion? Heck no! I found a fan that's lots quieter!

Our champion measured 12V 1082, 8V 715, 6V 510, 4V 250, 3.5V 176, and 3V 100.5RPM. I report the .5 because if I put down 100 you'd think I was making it up. 100.5 is the RPM I measured at 3V.

Again, a plot shows that this fan's motor controller IC goes to hell below 3.5V. But the 176RPM at 3.5V looks solid; I'd even be comfortable with a slightly lower voltage and 150RPM since the fan still runs at 100RPM.

A fan running 150RPM is 49.43dBA quieter than at 1000RPM by the 60*LOG10(rpm1/rpm2) rule. That, folks, is our champeen. And I have good reason to believe no other fan can come close to that figure. Why? Because in Devonavar's latest 120mm fan review, our champeen had by far the lowest power consumption at any given RPM. No other fan came remotely close.

[Since the fan did run at 100.5RPM, that's 59.87dBA lower than at 1000RPM, but I wouldn't trust the fan to run at that speed month after month.]

Ladeez and gennulmen, our low-noise champeen in the 120mm weight class: the Enermax Marathon fan with Enlobal bearings! I call it the magfan.

Mr Evil
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Post by Mr Evil » Sat Jun 30, 2007 11:16 am

Might adding weight to the blade tips allow the fan to run at slower speeds? It might give it enough momentum to keep turning between pushes from the motor.

Also PWM will probably work better than a constant voltage since it will be above the minimum voltage for the circuitry to operate for at least part of the time (using 5V pulses instead of 12V will allow a longer duty cycle for a given speed, which will probably be even better).

jaganath
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Post by jaganath » Sat Jun 30, 2007 12:15 pm

A fan running 150RPM is 49.43dBA quieter than at 1000RPM by the 60*LOG10(rpm1/rpm2) rule.
a couple of quick q's:

1) assuming this is true, does that mean if the fan is rated at 29dBA at 1krpm, it will emit -20.43dBA at 150rpm?

2) if that is also true, this will be substantially below the threshold of hearing will it not? it's hard to believe anything with moving parts can emit substantially less than 20 micropascals of sound pressure. I agree that the 60LOG rule is valid, but perhaps there is some kind of asympytote when one gets to these very low sound levels.

3) given that CFM scales with RPM, the airflow at 150rpm will be well into the low single-digits; anyone who can get by with this anemic airflow essentially has a fanless setup.

Felger Carbon
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Post by Felger Carbon » Sat Jun 30, 2007 12:39 pm

jaganath wrote:1) assuming this is true, does that mean if the fan is rated at 29dBA at 1krpm, it will emit -20.43dBA at 150rpm?
Yep.
jaganath wrote:2) if that is also true, this will be substantially below the threshold of hearing will it not?
Yes, at one meter. Remember, you're quoting 1 meter sound level measurements. Things get louder quickly at closer distances.
jaganath wrote:3) given that CFM scales with RPM, the airflow at 150rpm will be well into the low single-digits; anyone who can get by with this anemic airflow essentially has a fanless setup.
Again, you have accurately grasped the concept! :D

My new computer, using C'n'Q, draws 50W wall power at idle and 90W at load. Obviously, the CPU power at idle is very low indeed. Any HS you'd care to use will work passively at idle. The only time you need cooling air is when the CPU is under load. Ideally, you'd like to turn the fan off when idling.

The problem is, the fan then must be "goosed" with a 12V pulse to start it. If the fan is running at a very low speed, meaning very quietly, it need not be goosed to make it run faster under load.

This is obviously trespassing in CPU Cooling territory. I plan to write an article for that forum entitled "PWM? I don't need no stinkin' PWM!", but I need to run some experiments on actual PWM fans and gather some data first. Basicly, I'll take the PWM signal, process it with a very simple electronic circuit, and drive the Marathon champeen quiet fan's voltage supply to 3.5V when the PWM signal is "slow", and a higher voltage to be determined when the PWM signal is "high".

At 150RPM, the heat sink will, for all practical purposes, be purely passive. I don't think the fan will push enough CFM to cool a gnat! :D

continuum
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Post by continuum » Sat Jun 30, 2007 1:31 pm

At 150RPM, the heat sink will, for all practical purposes, be purely passive. I don't think the fan will push enough CFM to cool a gnat!
Which means this exercise, fascinating as it is, is largely for fun? :D

Still to think, all the "fanless" applications that overheat... the ones that need just a TINY bit of airflow... hmmmmmmmmmmmmm

Felger Carbon
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Post by Felger Carbon » Sat Jun 30, 2007 3:43 pm

continuum wrote:Which means this exercise, fascinating as it is, is largely for fun? :D
To the extent that I try to work a little fun into as many of my projects as I can, yes, partly for fun.

But my stated objective is absolutely serious. I want a fan that's immediately ready, without a goosed start cycle, to provide cooling air upon command. Until then, I want the fan to be as quiet as possible. I've found the 120mm fan that meets that goal.

There's also a little fun in that I've found a way to use the motherboard PWM signal to control a non-PWM fan's RPM. :D

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Post by aztec » Sun Jul 01, 2007 2:39 am

Felger,

any clue on where to get the 92mm version?

I've searched my favorite online stores and no dice.

Thanks!

Felger Carbon
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Post by Felger Carbon » Sun Jul 01, 2007 4:39 am

aztec wrote:any clue on where to get the 92mm version?
The 92mm version (UC9EB) appeared in very small numbers and then disappeared from the face of the earth. I think there was one pilot or preproduction or engineering sample run, whatever you want to call it. Those were sold (Directron had them briefly), and then they disappeared for good. The 80mm is available, and the 120 of course.

aztec
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Post by aztec » Wed Aug 01, 2007 1:39 pm

Felger,

sorry to bring up this older thread.

But @12v, would the Enermax be quieter or similar to a 120mm Nexus?

Its rated dBA is lower, but would be good to get your experience.

Thanks!

Felger Carbon
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Post by Felger Carbon » Wed Aug 01, 2007 3:13 pm

aztec wrote:@12v, would the Enermax be quieter or similar to a 120mm Nexus?
I have no experience with the Nexus. Both have very low bearing noise, on a par with the GW NCB (the Nexus uses Yate Loon bearings) :). So the one that pushes the most air at 12V will be the noisier, and that will almost certainly be the one with the highest RPM.

Since fans have a +/-10% RPM tolerance from nominal, the results of comparisons of specific fans will vary. Nominal is generally good for averages, but you cannot buy a nominal fan. :cry:

Running at 12V and depending on the nominal specifications is not wise. A better choice is the use of a fan controller. Since most controllers don't go all the way to 12V, if that top-end is important to you get an NCB - at 11V it will run at least as fast as the Nexus or Enermax.

cotdt
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Post by cotdt » Fri Aug 03, 2007 12:39 am

fascinating... but at such low airflow, you might as well go fanless...

charonme
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noise/cfm

Post by charonme » Fri Aug 03, 2007 1:22 am

but what people usually look for is noise/cfm, not noise/rpm or noise/volts...

cotdt
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Post by cotdt » Fri Aug 03, 2007 1:58 am

i think even chimney cooling will give more cfm, and without the motor noise

butters
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Post by butters » Fri Aug 03, 2007 6:19 am

Would 4 of these fans at 100 RPM be quieter than one of them at 400 RPM?

Felger Carbon
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Post by Felger Carbon » Fri Aug 03, 2007 8:59 am

butters wrote:Would 4 of these fans at 100 RPM be quieter than one of them at 400 RPM?
Keeping in mind this can only be calculated based on well-behaved bearings, 4 would be far quieter! By 30dBA, in fact.

To all of you who've noticed such a quiet fan is useless for cooling, congratulations! You have noticed the point of the exercise.

If we could eliminate bearing noise, which on a good fan is a lot lower than the "whoosh" noise at any RPM, then any useful air movement produces "whoosh". It's an energy situation: double the airflow, the "whoosh" noise goes up 18dBA. Halve the airflow, it goes down 18dBA. This is for one specific fan whose size never changes, of course.

The way to get quiet cooling is to use a larger fan, or more fans ("making" a larger fan out of multiple small fans). And this only works really well if you keep the gzins and gzouts balanced: air has to flow as well into the case as out, and out of the case as well as in. This is where some "big fan" cases fall down, such as the current Xclio 6030 Plus.

Do not wish for a small super-quiet fan that pushes useful cooling air: there is no such thing. Happy cooling! :P

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Post by ryboto » Fri Aug 03, 2007 10:09 am

I just used these fans in a friends new build, and I'm jealous. I wish they had been available back when I bought Scythe fans, they're cheaper and more quiet.

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