• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

120mm CPU fan for core i7 - PWM or regular?

S

Special K

Diamond Member
I am planning to build a core i7 rig with the EVGA X58 SLI and want to use the Prolimatech Megahalem as my cooler. The Megahalem doesn't come with a fan, so I will need to choose one of my own. I am looking for a 120mm fan and have seen two types: those that spin at a constant speed, and those that can use a variable speed via the motherboard's fan PWM control.

Which should I get? The X58 SLI has a 4-pin CPU fan header that supports PWM. I was considering the following options:

Fixed speed: Scythe S-FLEX series (link)

I was thinking about going with either the 1200 RPM or the 1600 RPM variant. I might do some mild overclocking, but I value a reasonably quiet PC and don't want any loud fans.

PWM fan: Scythe KAMA PWM (link)

This one spins in a range of 310-1200 RPM. Obviously the 1600 RPM fan would keep my CPU cooler than the PWM fan would at any speed, but the fan will be making the same amount of noise whether I'm just browsing the web or gaming. I guess that's not a problem if the 1600 RPM fan is really quiet to begin with, but I have no basis for comparison, as this is my first build.

So which fan should I go with? Do most people use standard or PWM fans with their CPU? A couple other questions I have:

1. Can I buy a 3-pin fan and connect it to a 4-pin CPU fan header?

2. If the answer to 1. is "yes", then can I control the speed of a 3-pin fan plugged into the 4-pin header using voltage as opposed to PWM?
 
1. Yes.
2. Sometimes. Some motherboards have a BIOS selection between PWM and Voltage under "PC Health Status" or something like that. Not familiar with i7 motherboards, so can't help you with that specific one.

Another option is to put your CPU fan on a separate fan controller. Some people don't like this, since there's no warning if the fan dies. What I've done in the past is split out the yellow wire (RPM sensor on most fans) to another 3-pin connector and plugged that into the CPU_FAN header. That way I can monitor the speed while still having full manual control.

Up to you. I personally love the S-Flex fans, I have two in my system right now. Haven't used the Kama PWM.

-z
 
Just plug it in. If you look at the motherboard fan connector, you'll notice a tab to one side. This is your guide for a standard 3-pin fan plug.
 
Thanks for posting this Special (and thanks zagood for replying) - I just decided on a Megahalem as well and am also trying to decide on a fan.

I'm planning on doing mild to moderate overclocking of my i7 920 but not even close to pushing the max, and I'm aiming to get a moderately quiet (but not extreme quiet) system. Sort of middle of the road all around.

1. Do you guys think its best to go with one fan or two? Or, to look at it differently, one medium speed fan, 2 low speed fans, or 2 medium speed fans? I wish I remembered the details of sound physics, I can't remember if decibels are strictly additive or not. Do two 12 db noise sources create 24 db of noise?

2. Zagoood - thats a very clever trick with splitting off the RPM sensor when using a fan controller! I don't know much about this but how bad is it if you didn't use the trick and had your fan on a controller, then if the fan died? I would have thought that the mobo would detect the CPU overheating and shut everything down before damage was done, even if it didn't have detection on the fan. Or is the idea more that the mobo will do this much faster (as soon as fan RPM drops to 0) with the trick, and thereby decrease the odds of causing damage?

3. Anyone else have thoughts on PWM vs. Fixed? (Thanks again Special K for starting this). I also have the same question about whether 1200 RPM on the KAMA is sufficient, and if 1600 RPM on the S-Flex is going to be significantly loud.


 
1. You can get better cooling for the same noise, or the same cooling with less noise, by using two fans. Two fans of the same decibel rating and noise signature together at half speed will (generally) produce fewer perceptible decibels than one fan at full speed. I can't remember the equation but I think it's something around two 12dBA sources creating 18dBA. You also have to consider that one is blowing directly against a heatsink, and other factors, but you get the idea.

2. Motherboards generally have a couple of different warnings - fan speed, fan fail, and temperature. Fan fail warning will keep you from getting to the temperature warning or throttling. Damage is unlikely as long as you have throttling or shutdown enabled, but you never want to get to that point if avoidable.

3. 1600 S-Flex at full speed isn't "significantly loud" but it's by no means quiet. Syzygies is using those so you can see his comments on the Megalahems thread. Personally I always get a little more fan than I need, use a controller, and if I need more oomph (when gaming or encoding) I just crank those puppies up.

EDIT: combined dBA actually much lower. Calculator here:
http://sphere.sourceforge.net/flik/misc/db.html
 
Originally posted by: trajan
1. Do you guys think its best to go with one fan or two? Or, to look at it differently, one medium speed fan, 2 low speed fans, or 2 medium speed fans? I wish I remembered the details of sound physics, I can't remember if decibels are strictly additive or not. Do two 12 db noise sources create 24 db of noise?
Click to expand...

I'm only going with one fan because I can't physically fit 2 on the mobo I'm planning to get (EVGA X58 SLI). I can't fit a fan on the left side of the heatsink because the VRM heatsink is in the way. I can apparently put one on the RAM side without blocking any RAM slots, as long as my RAM sticks don't have heat spreaders or heat pipes that extend up higher than the height of the RAM PCB itself. Supposedly 1 fan would provide adequate cooling.

I can't comment on the dB question, but it looks like zagood already answered that.

Originally posted by: trajan
3. Anyone else have thoughts on PWM vs. Fixed? (Thanks again Special K for starting this). I also have the same question about whether 1200 RPM on the KAMA is sufficient, and if 1600 RPM on the S-Flex is going to be significantly loud.
Click to expand...

I'm tempted to pick up the KAMA and a S-Flex. If the KAMA works fine in PWM mode when connected to the CPU fan header, I'll stick with it. Otherwise, I'll use the S-FLEX 1600 RPM fan, which I can always undervolt later. I'm just wondering whether a KAMA @ 1200 RPM sounds the same as a S-FLEX @ 1200 RPM. I don't think those two fans use the same internal components, but I could be wrong.

 
You might want to take a look at this fan:

Here

Be sure to checkout the specifications for this fan and there's a link to a review, which is worth looking at.
 
Originally posted by: Dodger1
You might want to take a look at this fan:

Here

Be sure to checkout the specifications for this fan and there's a link to a review, which is worth looking at.
Click to expand...

Wow, that is a very expensive fan.
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top