Everything changes with obstacles
To write that we have something mapped out to the last detail is perhaps too bold, but after proper preparation, few pieces of hardware are as easy to evaluate as fans. Of course, this had to be preceded by long preparations, developing a methodology, but you already know the story. What you don’t know yet is the first fruit, or rather the results of Akasa, SilentiumPC, SilverStone, Xigmatek or more exotic Reeven fans.
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 rotor) 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 31.5 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.
- Contents
- BeQuiet! Silent Wings 3 (BL066) in detail
- The basis of the methodology, the wind tunnel
- Mounting and vibration measurement
- Initial warm-up and speed recording
- Base 7 equal noise levels…
- .. and sound color (frequency characteristic)
- Static pressure measurement…
- … and airflow
- Everything changes with obstacles
- How we measure power draw and motor power
- Measuring the intensity (and power draw) of lighting
- Results: Speed
- Results: Airlow w/o obstacles
- Results: Airflow through a nylon filter
- Results: Airflow through a plastic filter
- Results: Airflow through a hexagonal grille
- Results: Airflow through a thinner radiator
- Results: Airflow through a thicker radiator
- Results: Static pressure w/o obstacles
- Results: Static pressure through a nylon filter
- Results: Static pressure through a plastic filter
- Results: Static pressure through a hexagonal grille
- Results: Static pressure through a thinner radiator
- Results: Static pressure through a thicker radiator
- Results: Static pressure, efficiency by orientation
- Reality vs. specifications
- Results: Frequency response of sound w/o obstacles
- Results: Frequency response of sound with a dust filter
- Results: Frequency response of sound with a hexagonal grille
- Results: Frequency response of sound with a radiator
- Results: Vibration, in total (3D vector length)
- Results: Vibration, X-axis
- Results: Vibration, Y-axis
- Results: Vibration, Z-axis
- Results: Power draw (and motor power)
- Results: Cooling performance per watt, airflow
- Results: Cooling performance per watt, static pressure
- Airflow per euro
- Static pressure per euro
- Results: Lighting – LED luminance and power draw
- Results: LED to motor power draw ratio
- Evaluation
I have this fan as a part of the Dark Rock Pro 4 cooler – the front one. The inner fan is disabled for now. Unfortunately, I am thinking about replacing it. What’s driving me completely nuts is the fan start that gives a sound resembling powerful rubbing against a rough surface. It’s okay for folks who want to have the fan running constantly and encounter it only during boot but I want to have a fanless idle – 0 noise, no vibrations, extended fan life, and lower power draw. I wish such behavior was stressed in this and other reviews so that one can find safe alternatives for such requirements.
It’s a pity to encounter such an unexpected drawback, as this fan is much quieter than Arctic P12. At 700 RPM, it’s barely audible in my Nanoxia Deep Silence 8 in the night, and below 500 RPM basically inaudible.
What you are describing is happening with several fans. To an excessive degree with the Strix XF120 as well, where we also mentioned it. I have thought about how to measurably grasp those starts in the context of the interpretation of the results so that a simple comparison across fans is possible, but I don’t know yet.. anyway, it will probably be an initial phase with rotor centering, which is accompanied by higher vibrations in addition to the acoustic expression.
Perhaps the evaluation page can be divided into several labelled subsections, one being dedicated to observations like this for example.
My P14 Slim rev.1 does this initially too, but it’s gone now after I have mounted it tight. Perhaps quality control and tolerance also play a role here?
Maybe we are each talking about a slightly different phenomenon. The initial, let’s say start-up sound of Strix XF120 will certainly not be influenced by the strength of the mounting. With this fan, it’s just that it takes some time (be it very short, in the lower units of seconds) to get centered, and the operational sound is probably a bit different after, let’s say, warming up. I would attribute this purely to the influence of the motor and the bearings. In this case, I would not talk about an issue of a single unit in serial production. Sure, within lower manufacturing tolerances some minor differences in behaviour can be present, but if that feature disappeared completely, I assume it would be due to larger, targeted changes in the design, which for example are solved by various revisions. Unfortunately, most manufacturers don’t talk about them, with a few exceptions (Arctic, for example). So sure, a Silent Wings 3 from the early batches may behave differently than the latest pieces from the current sales. And while we’re on the subject of fan differences from piece to piece, we’ll release one unconventional test in September that will be of interest to you. 🙂
I would rather attribute the different sound after tightening the P14 rev. 2 to vibrations and the fact that with a different mounting there may not be such significant resonance frequencies of the case.