The impeller is oriented so that, in the installed position, nothing visually obstructs the view. This refers to the stator struts, which can otherwise “spoil” the appearance. But this is not just about looks—it is about combining them with the efficient geometry of the proven five-blade design with a stabilizing ring (familiar from the P12 A-RGB). It is not exactly the same design, though, if only because what used to be behind the impeller is now in front of it.
Mounting and vibration measurement
Naturally, each tested fan must first be properly mounted. With all that we want to measure, and with the kind of precision that is required for relevant measurements, even the smallest details matter. The whole mounting system is quite complex and we are happy to have fine-tuned it to maximum satisfaction. Even if it meant hundreds of hours of tinkering. What’s so complicated about it? There’s more.
The fans are installed to the multi-purpose bracket. The substrate is a 2 mm thick metal plate to which the fan is attached, or the fan is attached together with an obstacle (e.g. a filter, hexagonal grille or liquid cooler radiator).
For correct and always equal pressure, the fans are always tightened with the same force with a torque screwdriver. If this were not the case, joints and clearances in the assembly could arise, in short, uneven conditions with undesirable distortion. For example, also for vibration measurement. On top of the fan mount there is also a bracket for the three-axis vibrometer sensor. The latter is magnetically attached via a steel insert, on which the sensor exerts a force of one kilogram and, thanks to the stop, is also always in the same place and in the same contact with the rest of the structure. These are the basics in terms of repeatability of measurements.
In order to capture the intensity at the highest possible resolution, the tray of the holder cannot be too heavy and at the same time it must be strong enough not to twist. This would again cause various distortions. Therefore, we used a hard (H19) aluminium (AL99.5) plate for the construction of the holder, whose weight is just enough so that free movement is not significantly restricted.
To achieve the finest possible resolution for vibration measurement, soft rubber inserts are provided in the mounting holes through which the bracket is installed to the tunnel. And just behind these inserts are silent blocks with a very low hardness of 30 Shore. These are also used so that the vibrations of the fans don’t spread to the tunnel skeleton. If this were to happen, then for fans with more intense vibrations, this secondary noise component, which is not related to the aerodynamic sound of the fan, would also be reflected in the noise measurement results.
This is where it is good to have ideal conditions, even though they are unattainable in practice, because fan vibrations will always be transmitted to the case skeleton to some degree. But each cabinet will react differently to them, or rather the final noise level will depend on a number of factors, starting with the materials used. Therefore, it is a good idea to filter out this extra noise component in tests and in practice take into account the measured vibration intensities. The higher these vibrations are, the higher the noise addition has to be taken into account.
The silent blocks are naturally formatted to offset the bracket a bit from the rest of the tunnel, otherwise they wouldn’t make sense. This creates a gap that is sealed across the entire surface with a soft foam seal with closed cell structure (i.e., it’s airtight).
To properly center the fan impeller in relation to the other elements, the bracket includes a protruding frame that follows the inner contour of the seal. And to make matters even more complicated, the frame with the tested fan is pressed against this seal by a small force of compression springs, which in turn is set with the highest possible resolution for vibration measurement in mind and at the same time so that sufficient pressure is generated to maintain a flawless seal.
Vibration is measured with a Landtek VM-6380 vibration meter. It records the vibration speed (in mm) per second in all axes (X, Y, Z). For quick orientation, we calculate a 3D vector from the measured values and graph the “total” vibration intensity. But you can also find your results if you are only interested in a specific axis.
The most complicated part of the tunnel is behind us, and we’ll move on in the next chapter. But we will still stay at the beginning of the tunnel, we will just turn to the peripheries on the sides.
Hmm, the 100th fan in the database—counting 140 mm models as well. On Thursday, we’ll do a kind of recap or summary, where all fans tested so far will appear together in the charts. 🙂
After reading the methodology section I’m still uncertain about when the tests were performed with the obstacles infront or behind the fan. Could you please clarify that?
Scenario by scenario, it varies. The radiators (both thinner and thicker ones) are behind the fans, as they are more commonly used in practice, while the dust filters (both nylon and plastic) are in front of them, i.e. in front of the impeller. That also makes more sense.
There is also a hexagonal grille in front of the fan, on the intake side, although in PC cases (for example, on the exhaust) it is often located behind it. We chose this placement because having it behind the impeller doesn’t change the acoustic profile very much, whereas with the opposite orientation, the difference can sometimes be quite significant, especially when it comes to tonal peaks. 🙂
Thanks for the clarification!
Your setup is what I was hoping for, for the reasons you already stated yourself. And just to make sure I’m not misunderstanding a fine detail: Whether **reverse blade fan or regular fan**, your dust filter test setup (both nylon an plastic) will always reflect typical real world usage, i.e. air will be “pulled” through the filter instead of being “pushed” through it. Right? Thanks in advance!
Yes, the dust filters are always on the intake side of the fans. 🙂
For the most accurate comparison possible, reverse fans are also positioned in the same relationship to the anemometer (in pull). That’s a more complicated discussion, but this is always the case regardless of the fan. If we did it the opposite way, in push, the area where we measure the wind/air speed—which is subsequently used to calculate the airflow in cubic units—would be too turbulent, and the results would therefore be distorted. 🙂