I'm considering an ASUS P8Z77-V motherboard for a new build and am also looking for some quiet case fans. I'm completely lost.

The motherboard has three 4-pin chassis fan headers. My understanding is that it uses PWM to control the speed of the fans (is that correct, or can it also do voltage regulation?). Do the fans have to be PWM? Do they need 4-pin connectors (what doe the 4th pin provide)? What happens with 3-pin fans?

What would be the ideal rated fan speed to take advantage of the fan regulation? Does it make any sense getting low speed fans when you have pretty good fan control, or are medium/high speed fans better?

I just, as in assembled/stated/went into BIOS, the LK version of this MB. It will control 4 or 3 pin case fans. No need for PWM. Right now I left the fan profiles at "Standard".

I am pretty sure that your motherboard can also control a 3-pin fan, but I am not completely sure.

The FanXpert can run fans between 40% (5V) and 100% (12V). So you'll need a fan that is quiet enough for you between 5 and 12 V. You'll also need to consider the starting voltage. If it's too high, then the fan can't be run quietly via FanXpert. That's the reason I'm a bit hesitant about buying a Nexus Real Silent 120 mm fan. May I recommend a Scythe SlipStream 800 rpm instead? At 5 V it runs dead silent (450 rpm or so), the starting voltage is about 3-4 V so you can be sure that it starts! At 12 V the fan can be heard but it's tolerable. So it behaves very well between 5 and 12 V.

So you'll need a fan that is quiet enough for you at 5 V or higher, and it needs to start reliable at your desired voltage.

The SlipStream 1200rpm can be heard at 5 V at 1m if you listen closely. It's very quiet, but I wouldn't recommend that fan if you're very sensitive to noise.

The advantage of PWM fans is that they have a wider speed range than 3 pin fans. For example the Scythe SY1225SL12LM-P has a range of 200 to 1300 rpm so it can give both a very quiet idle and still cope when the system is under heavy load. It also means that you don't have to take a risk on whether a low speed fan like the Slipstream 500 or 800 is going to provide enough airflow in high stress conditions. Or buy the Slipstream 1200 to cope with higher loads and hope the idle is quiet enough. The SY1225SL12LM-P can idle at lower speeds than all these fans and still go to 1300 rpm if required.

Thanks for the replies. I'm starting to get it. Actually, you've all mentioned the three fans I was considering.

Scythe SY1225SL12L 800 RPM
Scythe SY1225SL12M 1200 RPM
Scythe SY1225SL12LM-P PWM 1300 RPM

I keep reading about PWM fans having "bearing chatter" or somesuch that suggests to me that they can be noisier than voltage controlled fans. Is that something I should worry about? Also, the fact that Scythe only has one PWM model in the Slipstream line suggests to me that the vast majority of people are either using voltage control, or else no fan control at all.

I've read that Fan Xpert2 can run the fans as low as 20% of their rated speed. Is that true for both voltage control and for PWM?

As to startup speed... Since Fan Xpert is a Windows program, I would think that startup speed wouldn't be an issue unless you've also set the fan speed to be very low in the BIOS.

In my experience pwm fans can go slow without problems and 3 pin ones have a chance of low speed chatter. Not that I've tried them all of course but my cpu fans (kama flex 120mm 1600rpm) are pwm and work great but my 3 pin thermalrights acted funny at super low speed with my fan controller. I'll have them hooked up to an asus p8z77v-pro mobo with fan xpert 2 in 2 days so I can post back about how it went if you want.

I don't have an ASUS P8Z77-V with FanXpert, but I do have an Asus Sabertooth P-67 with some fan controller software included in the bios, and I notice that when the system boots up the fans go to full speed for a second or two before the bios fan control program kicks in, lowering the fan speed to the designated level. So the starting voltage "might" not be a problem with Asus FanXPert.

Fan Xpert / Xpert+ have limited control over fans utilizing a 3-pin connector. The newer Fan Xpert II supports 3-pin connectors and works with most ASUS motherboards, even though it isn't officially supported. I tried out Fan Xpert II on my ASUS P8Z77-M Pro and it worked without issues; however, I prefer Fan Xpert+ for now as it has some "dummy proofness" and I'm not well versed in fan control yet. I'll make the switch to Fan Xpert II when I learn more and get case fans with 4-pin PWM connectors.

Brando, how did that work out?

I really like it but it's not quite perfect. The fan controlling works great in every way except that the temp readings are off. Realtemp and hwmonitor show far higher cpu temps so I had to adjust for the discrepancy. It's not a huge deal as long as you can figure out what temps are actually real. I assume they'll patch this with an update at some point (I hope) but it can be worked around with a custom profile which isn't that hard. Also, now that I can see the minimum rpm I can confirm that my pwm cpu fans can run slower than the 3 pin fans. The scythe kama flex pwm fans can go down to just over 300rpm and the thermalright 3 pin fans can go down to about 500-550rpm (auto detect). With everything spinning at about 550rpm give or take the system is whisper quiet and I can only hear it if I put my head right next to it or it's under heavy load.

Now, what about CPU fans? These have been speed-controlled by motherboards for many years. How is that accomplished? Apparently not all by PWM.

I was just looking at some information on a Noctua CPU cooler and the fans don't appear to be PWM. They mention L.N.A. and U.L.N.A. ... what are these?

All of the fan headers are 4 pin but also accept 3 pin. Pretty sure you just switch to voltage mode.

Using a P8Z68-V here. The CPU fan header can only control PWM fans. 3-pin fans can plug into them and get power, but cannot be controlled. All the other fan headers (CHA_FAN, PWR_FAN etc.) can control both 3-pin and 4-pin PWM fans.

When I used a 3-pin fan (Scythe Kaze Maru 140mm) on the CPU fan header on my motherboard, I used a Noctua LNA adapter so that the fan spun at a constant rate - nice and quiet.