How Low Can You Go? (rpm-wise)

Bluefront · Post by **Bluefront** » Fri Jan 05, 2007 3:57 am

Fans are responsible for most computer noise, optical noise aside. So it makes sense to run your fans as slowly as possible, as slowly as necessary to keep the various components acceptably cool. Here is the problem....you need to find a way to get the fans to reliably start spinning at a low voltage, and maybe speed up when things become hotter.

A PWM control of fan voltage is one way..... this control can start and keep fans going at really low voltages, but frequently causes clicking, sometimes humming noises.

An analog voltage control is better from a noise stand-point, but many fans need a 12V burst to start spinning, before dropping back to a low voltage (say around 5v). And some fans will actually stop spinning when the voltage is reduced this low. So you need to actually run a fan at a straight 5v before you install the thing. Some analog controllers have a circuit that will raise the voltage till the fan starts spinning. An M-Cubed MINING acts like this.

But for a cheap controller I'm using a NoiseMagic NTM3, slightly modified with an extended sensor wire. This is an analog controller, plugs into the MB header between the board and the fan, and the MB is able to read the rpms (unlike the MINING). It gives the fan a 12v burst for a few seconds to get it spinning, then drops back to slightly under 5v. The temperature curve with this controller is 28-42C.

So with my setup today, the house at about 21C, the main fan a 120mm Scythe S-Flex 1600rpm model, the fan starts and runs at 475rpms, till the CPU heats up. Anybody able to start and run at a lower rpm with an analog control?

Aris · Post by **Aris** » Fri Jan 05, 2007 5:26 am

once the fan is inaudible from outside the case, whats the point of making it spin any slower?

i think my 2x nexus fans are spinning at around 600rpm, and they are completely inaudible from any distance from the case.

pcy · Post by **pcy** » Fri Jan 05, 2007 5:35 am

Hi,

I've got some 140mm fans down to 450rpm.

Even inside a case, and even at 600rpm or less, I have yet to find a genuinly inaudible fan.

If the room itself is sufficiently quiet...

Peter

Shaggy · Post by **Shaggy** » Fri Jan 05, 2007 6:00 am

Hi,
my 120mm globe fan starts perfectly, without any kickstart circuit, at 5V and it spins at 500 rpm at this voltage, but it is quiet at 700 rpm.
This fans works at very low voltage, some 80mm globe fans i have start at 3v, i haven`t tested the 120mm fan, but it should work at 3v with kickstart or after shortcut its thermal sensor, but this is unnecessary.

Aris · Post by **Aris** » Fri Jan 05, 2007 6:09 am

pcy wrote: Even inside a case, and even at 600rpm or less, I have yet to find a genuinly inaudible fan.

If the room itself is sufficiently quiet...

Peter

I jive against this point alot, because the point isnt to sit in an anabolic chamber with your computer in absolute silence. The point is to make your computer quiet enough that you cant hear it over the sounds you do want to hear. (ie: The tv, your music, your games, kids playing outside etc etc).

If i put my system in a very very low ambient acoustic space could i hear it? mabey, but it isnt, and it is effectivly inaudible with the noises i want to hear in the room.

If the fridge isnt on, and the fan in the room isnt on, and everything is off in my room, its very quiet. In that situation, you still have to get very close to the case and listen for it to hear it. If you were on the other side of the room sitting on the couch having a conversation with me while i powered my computer up with those ambient acoustic conditions of the room, you would not hear my computer turn on. That to me, is inaudible.

pcy · Post by **pcy** » Fri Jan 05, 2007 7:34 am

Hi,

The computers I build are used for recording music.

If I can hear it when everything else in the room is switched off it's too loud.

But "inaudible" means that you cannot hear it at all. That no the same as just quiet, or even so quiet that you don't notice it.

Peter

autoboy · Post by **autoboy** » Fri Jan 05, 2007 9:29 am

My Arctic Cooling Alpine 7 is on the 4 pin fan controler on my Abit NF-M2. It is only a 92mm fan and it is running 475rpm. It can keep my 3200+ at 60C @1.35V and full load. Not bad for 475rpm on a $10 heatsinks IMHO. Undervolted it runs the same rpms and 42C under full load.

The scythe Sflex 1200 is on the other fan controler and runs 500rpm. When i stopped the Sflex it did not start on its own. I had to give it a little help with my finger. I cannot stop the arctic cooling because the hub does not show (unless i turn it off i guess).

I can hear both fans in the system at night because it is in my bedroom. It is still very quiet. The loudest thing in the system is my 4200rpm toshiba 2.5in harddrive.

I must have gotten a really good fan in my nsk3300 power supply because I really can't hear anything but some ticking if I put my ear to it. Otherwise it is drowned out by the harddrive.

jaganath · Post by **jaganath** » Fri Jan 05, 2007 10:39 am

Even inside a case, and even at 600rpm or less, I have yet to find a genuinely inaudible fan.

Have you tried the new Noctua fans? Also as we discussed in the other thread any fan must make noise as a result of the way it moves air, so acoustic foam and baffled intakes and exhausts are necessary for true inaudibility.

cmthomson · Post by **cmthomson** » Fri Jan 05, 2007 4:24 pm

I use a couple of NMT-3 controllers and am very happy with them. BTW, you can connect an NMT-3 to a PWM header and it still works properly. The fan in my P180 power supply bay shares a SpeedFan grouping with the fan cooling my video card. The video fan runs at 600, and the power supply fan runs at 450. Both are Nexus.

A Nexus at 600 RPM (or a few of them like I have) are audible only within a couple of feet of the box. The faint buzz of my LCD power supply is all I can hear when the disks and DVD are inactive, and the house and neighborhood are quiet (6am sunday).

How would this compare to a studio? Well, rustling clothing and people breathing make more noise.

Bluefront · Post by **Bluefront** » Sat Jan 06, 2007 3:06 am

IMHO.....in a really quiet setting, noise from any fan will be heard. As the noise level increases in that location, fan noise becomes less of a factor. But for me, unless my parrot is making noise, or the TV is on, or the fridge in the next room is running, I can hear this Scythe running from three feet away, if the rpms go above about 800rpm. It's not motor noise.....it's airflow.

I don't need much airflow during idling conditions(much of the time).....675rpms is enough to keep this P4-3.4 about 32C, when the ambient is about 21C. 32C is a much lower temp than is needed......but there's the controller and it's temperature curve at work. Under extreme stressing the CPU will reach about 45C, with the fan speed having increased to 1250rpms or so.

What I'd really like is a controller/fan combination that would continue to idle about 500rpms, and rise in speed to keep the CPU around 45C max. I need about 1250rpms to achieve that from any 120mm fan. This Scythe/NoiseMagic combo is close to perfect.....but not quite. I'd also like to keep a slightly higher rpm possible....say for summer ambients. The 1600rpm Scythe should cover this ok.

As others have stated before....there's really no end to this quiet thing. But for me with this latest setup, I'm getting close.

Oh....to clarify this. This Scythe fan on the rear of the case is cooling the CPU/Ninja, the fanless Zen PSU, the NB/HR-05, and the various MB components. One fan blowing inward. Were this a dedicated CPU fan, I estimate the max rpm necessary would be less than 1000.

pcy · Post by **pcy** » Sat Jan 06, 2007 5:02 am

jaganath wrote:
Even inside a case, and even at 600rpm or less, I have yet to find a genuinely inaudible fan.
Have you tried the new Noctua fans? Also as we discussed in the other thread any fan must make noise as a result of the way it moves air, so acoustic foam and baffled intakes and exhausts are necessary for true inaudibility.

No, as it happens I have not. The quietest I have yet got is the 135mm Aerocool at about 450rpm.

But I can definately hear that from several feet away provided I stop breathing. That's not inside a case, of course. Also, the noise has all the characteristics of airflow, not bearing or mechanical noise. I find it unlikley that a different manufacturer will make any difference in this respect.

Peter

jaganath · Post by **jaganath** » Sat Jan 06, 2007 5:11 am

Of course, it goes without saying that the ultimate in inaudibility is fanless operation, however you need very low heat dissipation to go down that route, and it depends on the specific situation whether you can get sufficient performance from a fanless PC. The mCubed HFX series of cases are good examples of this.

Bluefront · Post by **Bluefront** » Sat Jan 06, 2007 5:31 am

Yeah....fanless operation is not an option, not at any reasonable expense with normal components. What is needed is a precise fan control, fans that can start and run slowly/quietly, but can rev up when necessary to keep the temps acceptable.

The Holy Grail for me....maybe within the realm of possibility.

Aris · Post by **Aris** » Sat Jan 06, 2007 8:02 am

autoboy wrote:I must have gotten a really good fan in my nsk3300 power supply because I really can't hear anything but some ticking if I put my ear to it. Otherwise it is drowned out by the harddrive.

I also have a 3300 and i dont think its just you. the psu fan in mine is also VERY quiet for a stock fan without modification. i was very surprised. i was planning on modding it out for an 80mm nexus, and decided to just start it up to make sure it worked first, and was amazed by how quiet it is. i have to put my ear right up to the case to hear it at all.

it probably doesnt hurt that my total system power draw is less than 100 watts though.

i can actually run the system completely fanless with no issue's with heat, but i cant hear the fans in my system from anywhere in my room no matter how quiet it is in the room, so for me its just add'd reasurance that i have nothing to worry about.

a recording studio chamber is the only instance i can think of that anyone would need a system that is completely inaudible. the rest of you guys are just obsessed i think. if you have to stop breathing to hear it when the case is open and your ear is right next to it, and still think thats too loud, you have issue's.

Atmosper · Post by **Atmosper** » Sat Jan 06, 2007 9:24 am

If you need completly inaudible, why don't you just put the computer in another room or a closet or something and just use an extender for the keyboard, mouse and display?

wpb · Post by **wpb** » Sat Jan 06, 2007 10:00 am

I'm happy with my set up. As a rookie to all of this, I went with a simple solution. First I bought a high quality, quiet case - Antec Solo.

PSU fan: Seasonic S-12 and the fan noise is almost inaudible to me. It's fine for me, and since I don't have the skill/know-how to mod it, I left it alone.

Exhaust & Intake case fans: Both are controlled by my Intel x975xbx MB. This MB has very efficient fan controllers and those 2 fans rarely exceed 700 rmps. The fans are soft mounted.

CPU fan: I changed the Intel stock HSF to a XP-90 with Nexus 92mm. Since the Nexus is a 3-pin, I undervolted it with a Zalman fan controller. It spins at less than 700 rpms, about the same as the 2 case fans.

Just a little encouragement to all the other newbies out there. These changes were all very easy to do and the reduction in noise is significant.

Bluefront · Post by **Bluefront** » Sun Jan 07, 2007 3:18 am

FWIW.....I've never been satisfied with the fan control system of any motherboard I've owned. I almost always install another fan controller of some sort. There is just not enough control available with the MB controller to satisfy me.

I guess I'm too picky.....but when it comes to silencing fan noise, you can always do better with your own fan control system. Takes some work to find the right combination however.

pcy · Post by **pcy** » Sun Jan 07, 2007 12:00 pm

Just changed th adjustment resistors on my PWM->DC converter to get a larger adjustment range, and I can now get the 135mm Aerocool to run at 240rpm.

Peter

NapalmDeath · Post by **NapalmDeath** » Wed Jan 10, 2007 8:19 am

I like the Zalman fanbus.
I tend to turn up fans late, and if ambient temps are higher (say Summer) I can ramp up sooner. Only 2 fans for me to control. (rear 120mm, and front 92mm) PSU has already been modded to a Nexus 120, and runs from 400-900 rpm based on heat. Sort of my backup should the rear 120 not do enough.

The NMT-3 is interesting, and I think I'll pick one up to test out.
On the 120mm Nexus rear right behind the Scythe Heatsink.

Ideally you have PWM with Speedfan, but I prefer my fan control independent of a windows program. Possibly one of those small programmable boxes you set once and let run.

kike_1974 · Post by **kike_1974** » Wed Jan 10, 2007 11:02 am

I think that a mixed PWM/analog can be used. With a very easy circuit at the PWM output (for example from the motherboard fan head), consisting in a resistor and a capacitor, this signal can be converted to a constant DC signal again (non pulses). It's a simple integrator.

With this approach you have the benefits of PWM (software controlled, for example) and the fan doesn't click anymore.

pcy · Post by **pcy** » Wed Jan 10, 2007 11:11 am

Hi,

Yes - it's not quite that simple as we found out when we tried to make them; but in principle that's all it is and the, final product is still pretty simple.

Peter