The maximum speed at which a fan spins is an important parameter, because the higher the speed, the more air it will be able to move (although, as we will see later, there are other factors that influence this in addition to its speed), but it will also have higher consumption and generate more noise.
These days it’s rare to find a fan that doesn’t have a 4-pin PWM connector, so its speed is automatically controlled based on the system temperature (the higher the temperature, the faster it will spin to exhaust more heat). (hot air and cool better). Connecting a fan to the card via a PWM connector usually also allows us to configure its speed via software, which gives us a great advantage because it will allow us to choose its balance between performance and volume.
In general, you should look at your fan speeds in the specs to determine this balance between performance and noise, or at least configure it appropriately through software. Here’s an example: A 120mm fan running at 1000 RPM or less is virtually inaudible when mounted in a closed PC case. For 140mm fans, this inflection point is around 800 RPM.
Size
Although the most common sizes for PCs are 120 and 140mm, there are actually fans of all sizes, from 40mm to 200mm and even larger. The bigger the fan, the more air it will be able to move with less speed, so in this case, the bigger the fan is usually better.
If you look at the image we posted above, the size of the rotor cover (that circular piece in the center) is always the same size, meaning the smaller the fan, the less space it will have for the blades, which are what really move the air. For this reason, a smaller fan will generally spin at a higher speed to move more air and will therefore make more noise.
For example, generally speaking, a 200mm fan only needs to spin at 400rpm to move the same amount of air as a 120mm fan at 1000rpm.
Air flow
This is one of the most important PC fan specifications because airflow measures how much air it is capable of moving and, therefore, its cooling power. It is generally measured in FCMwhich means cubic feet per minute, although it is also common to see this characteristic measured in liters per minute or cubic meters per hour (m³/hour).
It is obvious that when we talk about fan specifications, the greater the airflow or flow rate, the better as it will be able to circulate a greater amount of air, thereby increasing its cooling capacity.
We could tell you that 1 CFM is about 1.7 m³/h, but we’re not going to exaggerate: just keep in mind that the higher this value, the fan moves more air and therefore has more better performance.
Static pressure
Static pressure could be defined as the power of the fan, the force with which it is able to push the air. This is particularly important when the fan is to be installed on a heatsink or radiator, as it will need to push air through the fins of these, i.e. it will have an obstacle right in front of it. The more static pressure it is able to generate, the further the air will travel through the heatsink or radiator and therefore cool better.
Static pressure is usually measured in mmH2O or even in Pa (pascals), and is equivalent to the height of a column of water that the fan would be able to lift if it operated submerged at the edge of a body of water. A bit complicated to understand explained like this, but keep in mind that the higher the static pressure of a fan, the more power it will have and it will be much better to install it on heatsinks and radiators.
In fact, fans that come with heatsinks and radiators typically have high static pressure compared to fans designed to be installed in the PC case. What static pressure value is considered high? Well, you could say that from 2mm H2O.
Noise
Among the technical specifications of PC fans, we will almost always also find noise, generally determined in dBA. This measurement corresponds to the decibels that the fan emits “in the air” (that is, without being installed in a PC) at a distance of exactly 50 centimeters, and normally they will always tell us what its maximum noise is , operating at maximum speed.
Of course, how much noise is excessive? How do you know if a fan is quiet? For this we have the following table, and as you will see the dBA scale is not arithmetic but logarithmic, so for example 80 dBA is twice as loud as 70 dBA:
| sound source | dB | Effect |
|---|---|---|
| Plane taking off at 25 meters | 150 | Rupture of eardrums |
| Airport takeoff runway | 140 | Pain threshold |
| Takeoff of a military fighter at 20 meters | 130 | Pain. This is 32 times more intensity than 70 dBA. |
| Truck horn at 1 meter. Live concert. | 110 | Average human pain. 16 times more intensity than 70 dBA. |
| Electric lawn mower. Helicopter at 30 meters. | 100 | Eight times more intensity than 70 dBA. Maintaining this level for 8 hours causes damage to the eardrums. |
| Motorcycle at 10 meters | 90 | 4 times more intensity than 70 dBA. It can damage eardrums if exposed for more than 8 hours. |
| Dishwasher. Factory (average). | 80 | Double the intensity to 70 dBA. Threshold of what is usually boring. |
| TV sound | 70 | Due to this intensity, it is already annoying for many people. |
| Conversation in a restaurant | 60 | Half the intensity of 70 dBA. |
| Normal conversation in a house. | 50 | Four times less intense than 70 dBA. |
| Library | 40 | One eighth of the intensity of 70 dBA. |
| Campaign | 30 | Sixteen times less intense than 70 dBA. |
| Whisper | 20 | Barely audible if you’re not very close. |
| Breathing | ten | Inaudible to most. Human beings do not normally listen to their own breathing. |
| Absolute silence | 0 | It is literally impossible for a human being to “hear” absolute silence, but it is the threshold of hearing. |
Personally, we will tell you that a fan below 30 dBA can be considered quite quiet. Above this value, no matter what the scale tells us to the contrary, it is already a fan that is “noticeable” when running on the PC.
One thing to keep in mind is that the noise made by a fan generally has more to do with the shape and arrangement of the blades and the air they move than the noise made by the motor. .. the fan motor is generally very quiet. , and the noise they emit is that of the air passing through the blades.
The shape and number of blades
Although this is not typically a fan specification, we want to talk to you about it because understanding the arrangement of fan blades is important to understanding how they work.
Normally, fans usually have between 5 and 11 blades (and it’s almost always an odd number, i.e. there are fans with 5, 7, 9 and 11 blades but you will rarely find fans with with 6, 8 or 10), and because you will assume that the more blades they have, the closer together they are or the thinner they are, and in the same way, the fewer blades the fan has, or they are more spaced apart or wider .
What we must remember from this is that when the blades are wider, it is to move a greater quantity of air, that is to say that we would be talking about a fan in which air flow (CFM) takes precedence over static pressure. But be careful, because the inclination of the blades also comes into play here: the more they are inclined, the more static pressure they will generate (mm H2O), i.e. they will be able to push the air further.
Then, whether it has more or fewer blades or whether the separation between them depends on how the manufacturer wanted to design it, in the same way that there are other factors such as whether the blades are joined together. at the end to reduce turbulence, etc., and all of this also influences (although to a lesser extent) fan performance, airflow, static pressure, noise, etc.
Table of Contents
