I'm hoping someone can give me a background on how the algorithms for CPU Fan speed generally work. I'd like to know if for my system the CPU fan speed is based on system load/CPU clock cycle (Turbo Boost) or if it's just based on actual CPU temperature.

To give you background of what I'm trying to figure out - I built an i5 760 system with a Gigabyte P55-USB3 motherboard back in September. I have been very happy with how quiet it's been - a large open case with large fans, an effecient processor that tends to run cool, and a small stock/box CPU fan that usually doesn't need to work that hard, and thus is quiet. I'm sure the fan runs a little faster and louder when I'm playing games, but in that case I'm not going to tend to notice the additional noise, regardless.

Over the past couple days, I've noticed the irritating high pitch noise of the stock fan when I'm not heavily using the computer - just simple browsing, for example. I'm not sure what changed. I have a few theories, but I need to know what the feedback for the fan speed algorithm is - temperature, load, or clock cycle - to verify my theories. It's spring time and it's started to get warmer. I have a bit of a dust issue and I just tried to clean out some of the dust in the CPU Heat Sink with limited success (I'll see if I can get an air can to help next week), so those would explain higher temps. It's also possible that there are issues with the bearings (?) I also greatly reduced the noise level on another computer a few months ago, so it's possible that I'm crazy - this noise was always there I just didn't notice it before. I might want to look into non-stock solutions, as well.

After posting this I realized one more (maybe more likely) possibility...

I think the big difference *if* nothing (dust, etc.) changed, is the fact that as spring has arrived, the louder noise of our HVAC fans pumping wintertime heat has left.

The Intel stock cooler isn't really a good one. While its able to keep the CPU from burning its not quiet. Definitely swap that for a recommended model as soon as you can. The minimum fan speed on that is typically ~800 RPM or higher, and since its so small temps would rise and fan speed would ramp up even on low loads.

As for how speed is controlled, from what I've seen its temps. Applying even a slight load has an immediate effect on temps and thus may affect fan speed.
Different motherboards control the fan speed in various ways. I had an Asus board that never ramped up the fan even on full load (temps in mid 60s), now on my Intel board I can define what the fan does at what temps in the BIOS. I opt to keep it under 600 unless it goes over 70c then it starts ramping. AFAIK Turbo boost has nothing to do with fan speeds.

Consider getting an SPCR recommended after market cooler and running it will a slow constant speed fan. Any Noctua, running the fans at their slowest speed will do well. Simple, Crude, Effective.

If cooling performance is a concern the top rated Noctua NH-D14 is a good choice. It is about as good as you can get... and it cools not only your CPU but other board components as well. But there is no Noctua that is a bad choice.

See:
http://www.silentpcreview.com/Recommended_Heatsinks

Please note that any comments about noise relate to running the fans at other than their slowest speed. Even at their highest speed, they will be way quieter than the stock fan. Even at their lowest speed they will be way cooler than the stock heat sink.

As new heatsinks come out Noctua provides its existing customers with new mounting kits for free. Very good after market service.

Okay, so I'm mainly looking at 3 HSF combos of the recommended list. They all are about the same price:

• Thermalright Ultra120 eXtreme
• Zalman CNPS10X Quiet CPU Cooler
• Noctua 120mm SSO CPU Cooler

All 3 come with fans and my preference is to use stock if it's acceptably quiet so I don't have to mess around with much. I'd like something that can use the same adaptive speed control that the LGA 1155 and 1156 motherboards give to the stock fans - it seems to be a nice, useful feature. I'm not sure which, though.

Here is what I'm thinking - let me know if you have any thoughts or can verify/contradict mine:
The Zalman doesn't have any speed variability. It also was reviewed here as having a lot of noise. I'm not sure about the Thermalright and Noctua stock fans having variable control. I worry that the Noctua is overkill with two fans, maybe generating more cooling and noise than I need.

All 3 are capable of doing a good job.

However, using their stock fans is not always the best choice. It might work great with the noctua, but I think you might want to swap the fan on the TR or Zalman if you get one of them. Most motherboard CPU fan headers use PWM to control the fan speed, so you'll want a PWM fan for best control.

Just set the fans to their lowest speed and forget them. You will be OK. If you really want, remove one of the fans.

So with these, people are just getting something so overpowered they don't have to worry about the variable speed control? They just set them on the lowest setting, and even at full load they are fine?

Your system is designed to use a PWM fan. So if you were to pair say the Thermalright Ultra120 eXtreme with Scythe's SY1225SL12LM-P PWM fan you should find that, in PWM mode, idle speed will be in the 400 -500 rpm range, effectively silent. This is possible because at idle your CPU will by default both underclock and undervolt. Since PWM fan control is essentially thermal, driven by the temperature of the CPU and individual CPU cores, when there is little or no load on the system the fan will drop to very low levels. Any increase in CPU temperature will result in a rise in fan revs, and this can result from a combination of ambient temperature, temperature inside the case and the load on the system particularly from a gaming graphics cards.

In practice you might see a maximum increase to around 1100 rpm with a top end graphics card playing a very demanding game, and maybe a touch more if you overclock your CPU. The advantage of enabling PWM fan control is that it is 'fit and forget'. At idle the CPU fan will not be heard, and even if it runs a bit faster under a heavy gaming load you're still unlikely to hear it.

The other thing that you can do with a PWM fan, if you wish, is to use the board manufacturer's software to control how the PWM fan responds. In the case of Gigabyte this is the Intel version of their Easy Tune6 utility. This will allow control of the PWM fan speeds based on temperature break points that you set. There are third party alternatives to such motherboard manufacturer's utilities including SpeedFan.

Thank's lodestar. Yes, I agree, adaptive cooling. You answered my original question - heat based, not load based - and it's cool to know that I have an option of adjusting the algorithm (don't know if I'll ever want to). So I need to figure out which stock fans come with decent PWM fans...

I don't think the Zalman does, but there is one person claiming the Thermalright does. I'm not sure about the Noctua, but my guess from comments in this thread is no. Sounds like the Thermalright might be what I want. It's too bad SPCR only reviewed the HS, not the fan.

On an off-topic note, I was curious to know what makes a PWM fan a PWM fan. LOL, I found it amusing that the 4th wire is just a continuous power wire to allow the speed sensing feedback to continue to work: http://www.analog.com/library/analogDia ... speed.html So really any fan could be come a PWM fan...

I'm beginning to doubt that any of the three have PWM with their stock fans...

I don't think they do. I think the noctua typically has 2 adapters for low and ultra low speeds. It's probably the best choice out of the 3.

I'll look into a HS only option and then look for a separate PWM fan. I guess I'm not really in a big hurry right now anyway - I'm working on putting together another computer.

I was at Microcenter yesterday, picking up the mobo and cpu for the new i3 sandy bridge I'm building for my wife. I was looking at the open box area and I saw what of the thermalright ultra 120s (open box for $30 - at that price I almost bought it but I wasn't certain it came with an LGA1155 mounting kit and it clearly stated all sales were final).

While I'd seen the SPCR reviews that show it's size relative to the stock processor, it's scarier to see how big they actually are in person. I'm balking at the idea of getting a 120mm cooler, now. It just seems like overkill (LOL). I have a hard time imagining putting something that big in either of these systems even though it would fit (just barely in the smaller case). There already are large fans in that area of the case and a lot of airflow, and the stock cooler is normally more than quiet enough. We'll see. I'll look around to see if I can find an acceptably quiet PWM solution that is between stock and the 120mm options. The stock's pitch is unacceptably irritating on occasion when just while browsing. I might be okay with such noise if it only were when I was really taxing the system.

I'll get an air can and see if blowing out the dust accumulated in the HS in just 9 months of use causes any noticeable changes, too - it's worth it just to know.

Considering the Scythe SCSMZ-2000 92mm (believe it should be the same as the Scythe Samurai ZZ reviewed on SPCR) but it is supposed to be loud at higher speeds. I'm not sure how much of an improvement over the stock it is - perhaps better thermal performance pushes the heat vs load curve downwards so it doesn't hit those high speeds as often, which would definitely be a plus.

Yes, the SCSMZ-2000/Samurai ZZ are one and the same. Another 92mm fan CPU cooler you could consider is the Cooler Master Hyper TX3 http://www.microcenter.com/single_product_results.phtml?product_id=0312368. It is 1156/1155 socket compatible.

Thanks loadstar, I'll look around to see what reviews and good things I can find about the Hyper TX3.

The Scythe SCMG-2100 Sleeve CPU Cooler is probably a better option than the other 3 120mm options I listed - it actually comes with a good scythe 120mm PWM fan and costs $43 at Newegg, $38 at Directron. I might have to cross reference more of the SPCR recommended HSFs against Newegg - it looks like many that aren't listed as LGA 1155/1156 compatible actually are, they just haven't been updated, so I probably have more options than I realized.

That scmg2100 cooler looks identicals to Mugen 2 - an excellent cooler. The fan is one of the best PWM fans available. I'd go for it.

Because that scmg2100 IS the Mugen 2.

Alright, I bought one of each of the PWM Scythes:

The Scythe SCMG-2100 120mm for $39 after promo + shipping (just a hair under directron, which is another place I love).

The Scythe SCSMZ-2000 92mm for $32.70 after promo + shipping (best deal I could find).

A Newegg promo code that expires on 4/25 for 10% off CPU coolers was the catalyst (EMCKFJE36). Add that plus $45 for Portal 2, comes to $116.47 all together. I have to computers to put them in and either one should fit in either computer (the LGA 1155 i3 2100 or the LGA 1156 i5 760). I'll let you know how it goes!

On a side note, while messing around with the computers and verifying much of the noise was coming from both of the HSFs, I noticed that I didn't quite have the HSs on there tight. I didn't read the directions carefully and turned that extra quarter turn that is shown on the mounting tops (which is supposed to be a RELEASE not a LOCK) X-D I've been running the i5 760 like this for around 7 or 8 months! Unfortunately or fortunately it didn't seem to have a major impact - fan speed, noise, and temps seemed approximately the same (yes, I completely reapplied the HS, including arctic silver thermal compound and all).