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.
- Each piece has different vibrations
- Results: Vibration, in total (3D vector length)
- Results: Vibration, X-axis
- Results: Vibration, Y-axis
- Results: Vibration, Z-axis