This is a first – a fan with the leading edges of the impeller blades on the opposite side to normal ones. This is primarily done for a better view of “fans without stator struts” in cases with glass side panels. In addition, such an unconventional design also has quite clear and measurable advantages and disadvantages, also in terms of functional characteristics. Let’s take everything in turn.
Everything changes with obstacles
So far, we have described how static pressure and airflow measurements are made under conditions where the fan has no obstacles in its path. In practice, however, fans do not usually blow into an empty space, but have a filter, grille or radiator in front of or behind them, the fins of which need to be pushed through as efficiently as possible.
We will also measure both airflow and pressure through practical obstacles for the reasons stated above. These include two types of filters that are usually used in PC cases. One fine – nylon and the other plastic with a thinner mesh. One other obstacle is the hexagonal grille perforated at 50%, on which the vast majority of fans – intake and exhaust – are installed. In some cases, we measure the effect of the obstacles on the results at positions (behind or in front of the impeller) that are used in practice. All obstacles are both pushed through to detect pressure drops, but also pulled through, which in turn speaks to the impact on airflow.
We use two radiators that differ in thickness and fin density. The EK CoolStream SE120/140 is 28 mm thick and the FPI is 22, the Alphacool NexXxoS XT45 v2 is thicker (45 mm) but with less FPI. CoolStream’s fin disposition is also similar in parameters to AIOs. The results on the NexXxoS will again be attractive for those who build their own water cooling loops, where the fans should work well even at low speeds – hence the lower fin density.
These obstacles and especially the radiators, but also the grilles, increase the mechanical resistance in front of the fan, resulting in higher noise levels. However, we will still tune the fan speeds to the specified noise levels of 31 to 45 dBA. Naturally, the speeds will always be lower than when testing without obstructions, but we will maintain the noise levels for clarity. The different noise levels with and without obstacles will only be at maximum power. In this mode it will also be nice to see how the fan design works with the obstacle and in which case the noise level increases more and in which less.
That’s unexpected results. I would have guessed it performs better on radiators than vs no obstacles, but it’s the opposite!
Is the buzzing noise only present under ~750 RPM, or is it there across the whole speed range? On higher dBA settings, I can still see some of the peaks at 1-2 Khz.
There will probably be some buzzing at higher speeds, but because of the diminishing contribution to the total, in contrast with the aerodynamic noise (which drowns out these sounds) it fades out alongside other, significantly noisier frequencies. The buzzing is, of course, more pronounced at lower speeds (like ~750 rpm), at the limit of minimum rpm. But we don’t have a spectrogram for those. 🙂
Noticeable buzzing noise is present till the 20% of PWM or ~660RPM, have three of those on a 45mm rad :/
I mean buzzing is starting from 20% of PWM and 660RPM, and after 800-900RPM buzzing noise doesn’t bother because airflow noise is louder.
Little correction 🙂
Thank you for sharing your user experience. Yes, the buzzing noise also occurs at higher speeds, and the question is to what extent it is disruptive at which speed compared to the aerodynamic noise. This can be evaluated differently by everyone, as it is subjective.