Sunday, August 9, 2009

Hexagon v3: Part 2 – Case fans

This is a post about my new custom build PC. To see all posts, check out Hexagon v3: Part 1 – Main Components


When it comes to cooling, there are two characteristics that are mutually excluded. You want to fans to be silent, means you don’t hear them. On the other hand, your computer wants as much fresh air as it can get which means the fan should run at full power. And this causes noise.

The problem is based how fans work: An engine will spin a propeller that will blow fresh air to the area you need it. The higher the need of fresh air (air flow, measured in CFM – cubic feet per minute), the faster the propeller needs to spin. And this will simply cause more noise. An example might help:

A Silent Eagle SE 120mm (which is designed to be silent) run at 12 volts will spin at 1250 RPM (rounds per minute) and has a loudness of 1,1 Sone. This means: It has a loudness of “very calm talking”. You can hear it, but it’s not disturbing. The air flow of it is in this case 26 CFM.

If you now slow this fan down to 9 volts, it will spin with only 750 RPM and its loudness will go below 0.1 Sone. This means: It has a loudness of “calm breathing”, equals “You just can’t hear it” equals “Silence”. However, the air flow is reduced to 19 CFM.

To have the same air flow (CFM) as before, you would need two fans (38 CFM in total), but still completely silent.

To have a good air flow but also a silent operation, you should go for a fan that is running at low RPMs. To balance the reduced air flow, simply add more fans.

(I should add that an even better solution is to use a bigger fan, for example replacing a 120mm with a 200mm model. However, given how cases are build today, this isn’t an option. If the case expects a 120mm fan, you just can’t install a 200mm fan.)


That was also the reason why I choose the Antec Twelve Hundred as my case: It has three 120mm fans in front, two 120mm at the back and one 200mm fan on the top. The only problem with the fans that Antec delivers: You can only switch them between Low, Medium and High. Even when set to “Low”, the 120mm fans are running with 1200 rpm which is far too much for me. The 200mm fan on top of the case runs at “Low” 400 rpm (82 CFM) so this should not be a problem.

I know currently of exactly two fans that have a good airflow together with a silent operation:


be quiet! SilentWings USC 120mm (My number one choice)

Comes with 3-pin connector (not 4-pin for PMW!), 7V adapter to 4-pin Molex (7 volt, 900 RPM) and a 12V adapter to 4-pin Molex (12 volt, 1500 RPM). The fan case is decoupled, so vibrations will not cause more noise.

imageSharkoon Silent Eagle SE

Comes with several adapter cables :  "Standard": 4-pin to 4-pin PWM (color: white), "Low Noise" (black): 4-pin to 4-pin Molex 12V (1250 RPM), "Silent" (red): 4-pin to 4-pin Molex 9V (750 RPM) and "Ultra Silent" (blue): 4-pin to 4-pin Molex 7V (300 RPM).

I choose the SilentWings over the Silent Eagle SE for a simple reason: When run in silent mode (7V for the SilentWings, 9V for the Silent Eagle SE), the SilentWings is running at 900 RPM while the Silent Eagle SE is running at 750 RPM. This means that the SilentWings has a better air flow with more CFM.

 cooler3One more thing: When installing a fan, always make sure the install it in the right direction. Yes, I know this must sound odd but I also installed a fan in the wrong direction once. Simply have a look at the fan you want to install and check the arrows every fan has (click the picture to enlarge it).

This SilentWings has two arrows: The arrow on the left points to left and indicates that this is the direction the propeller is moving (in this case, to the left). The right arrow shows you in which direction the airflow is. In this case, the airflow will be bottom up, this means the fan will accelerate the air from the bottom to to the top.

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