Each piece has different vibrations
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Each piece has different vibrations
Like all products, fans have some manufacturing tolerances. These determine to what extent some of the engineering details can vary across samples. Well, this should be the case, although it is possible that in practice there are often no funds left for a proper output check.
Higher manufacturing tolerances can naturally be expected for fans on the more inexpensive side, or we expect that the results of individual samples will vary more from piece to piece than for 2-3 times more expensive models. Of course, this may not always be the case, but in our experience, on average, the proportionality holds true that the differences in vibration increase with lower price if two different pieces of the same fan model are compared at the same speed. This is also why we work with at least two samples in our measurements, and if the difference in measured values is too high, we add a third sample. That’s usually the case with cheap fans, which include the Endrofy Stratus 120 PWM, codenamed EY4A007. At a price of around 6 EUR, we don’t want to criticize them for anything, and although they will get the brunt of it now, because they are being pointed out, later you will see that similar and even worse results will apply to other models as well.
In the following sections of the article, we will analyze 15 pieces of the aforementioned fan (Stratus 120 PWM), which are made up of a random selection from a store. Based on our vibration measurements, the way we are doing them, a set of results will emerge that can be arranged from lowest to highest. This will create a kind of variance given by, among other things, the median. That is to say, the middle value of the measurements. But it will also show how much the least vibrating sample may differ from the one that vibrates the most.
And why measure vibrations and not something else? Because it is this parameter that best reflects the differences in machine production. Measuring anything else at the same speed would give you significantly smaller, always negligible differences. But the variance of vibration, on the other hand, is wide, and all the more so when the measurements are very sensitive, with high resolution.
Methodologically, we reserved six modes for testing, defined by equal speeds, 600, 800, 1000, 1200, 1400 and 1600 rpm. We normally test fans in modes normalized by equal noise levels, but for these purposes we consider speed to be a more appropriate variable. This is for the reason that the measurements are not affected by small nuances in the varying noise levels. Its values do not vary much in our case because the fan is isolated from the rest of the tunnel by a soft “pad”, which makes the secondary noise (amplified by the rest of the structure of builds in which the fans operate) practically non-existent, but even so, as far as vibration analysis is concerned, the more accurate method is to test at the same speed. These are set using the UNI-T UT372 laser tachometer.
Fan speeds always naturally fluctuate a bit over time (on the order of units of rpm), even with “fixed” power supply. On average, after settling, we need to stay at a given speed within one decimal place (so for example 1000.0 rpm) and only then do we start to record vibration measurements. Their values are also averaged and the average values are recorded in the graphs.
Vibration is measured with the Landtek VM-6380 tri-axial vibrometer in the way we do in fan tests as standard. From the partial data for each axis (Chapter 3–5), a 3D vector (Chapter 2) is then computed, which refers to the total vibration.
Individual Endorfy Stratus 120 PWM fan pieces labeled as samples 1–15, with the relatively “worst” piece being red and the “best” being gold. However, you will only come across the latter within the chart pop-up after the cursor hits the “sample 3” box, where the corresponding bar is not displayed as it is numerically registered with a value of 0.00 (i.e. no measurable vibration on the frame). A verbal interpretation of the results can be found traditionally in the final chapter of the article.
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Results: Vibration, in total (3D vector length)
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Results: Vibration, X-axis
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Vibrácie, os Y
Results: Vibration, Y-axis
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Results: Vibration, Z-axis
Same model, different pieces. Differences in vibrations can be dramatic. Especially if they are cheap fans with high manufacturing tolerances. While most Endorfy Stratus 120 PWM fans have some vibration, you can also come across “golden” samples that don’t vibrate at all. This is admittedly a very rare but existing situation. The variance of vibration is much greater than you might think.
Conclusion
The differences in vibrations across different pieces of Endorfy Stratus 120 PWM fans can be diametrical. Basically from no vibration on the frame to higher vibration, but never downright high. If you go through the database of vibration results of other fan models, you’ll find that even the Stratus 120 PWM sample (6) with the most intense vibration still fares better than the Arctic BioniX 120 A-RGB or the Cooler Master Mobius 120 OC, which even has a hoop to damp vibrations caused by overly flexible blades. So why does it vibrate significantly? Because the vibration is caused by a different reason than on the Stratus 120 PWM.
We’ve discussed a number of causes for fan vibration in this article, and in the case of the cheap Endorfy fan in particular it seems to be poorer rotor centering. Or rather, depending on the sample. The variance in the widest band, at 1400 rpm, is 0.00–0.263 mm/s. Some samples achieve relatively worse results even at lower 1200 rpm. We assume that the main source of Stratus 120 PWM vibrations is the varying precision of rotor mounting, which is also affected to a large extent by the quality characteristics of the axle. It is probably the quality characteristics of the latter that determines most whether a particular piece vibrates more or less than another. It depends on the accuracy of its position on the center, but also on whether or not it is perfectly straight.
If you visually compare the piece with the lowest vibration (sample 3) and the highest (sample 6) you will find nothing to suggest that each fan vibrates slightly differently. The weight is the same and the build quality is no different either. The edges of the blades are also nicely smooth. In short, on the outside one appears exactly like the other and the quality differences are hidden on the inside.
The vibrations from the undulations at the end of the blades obviously don’t transfer much to the frame. If this were the case, it would not happen that we measure 0.00 mm/s on one sample (3). Nevertheless, some vibration does occur at the blades. Too weak to reach the frame, but at the same time of a frequency sufficient to produce tonal peaks at low frequencies of sound. These are comparable for all fans, regardless of whether it is the piece with the lowest or highest vibrations.
Of course, pieces with higher vibrations may have a significantly different sound, but this will already vary from use case to use case. It depends on how the fan vibration on the frame will react in combination with the particular case or cooler they are mounted on. While in one environment they may get into resonant frequencies with annoying tonal peaks, in another they may not. You can’t really deduce the intensity of vibration without using a vibrometer, only based on frequency analysis of the sound, although you may come across such hypotheses in the public space. A noisier fan, with higher tonal peaks, may well have lower vibrations (even if they are purely blade-level vibrations) than a quieter fan that vibrates more, but outside the most critical resonant frequencies. We’ll cover this in more detail, it would be a bit off topic now.
So yes, with cheap fan models it makes sense to rummage through a little, qualitatively you can come across different pieces. Later on, we’ll repeat similar tests with more expensive fans with more robust axles and you’ll see that there will already be significantly smaller differences between them. We already know this based on the fact that with all the fans we test, we rely on multiple samples. And high-end models such as the Noctua NF-A12x25 (PWM), the Phanteks T30 or the BeQuiet! Silent Wings (Pro) 4 do not differ much in this respect and scale very well with each other.
English translation and edit by Jozef Dudáš