Silent Wings Pro 4 (BL098) in-depth review: Hard BeQuiet! KO

BeQuiet! Silent Wings Pro 4 (BL098) in detail

All the secrets around the BeQuiet! Silent Wings (Pro) 4 are over and the detailed analyses of the sub-features begin. And it’s great that we can be a part of it. This is, after all, without a doubt, the biggest “cooling” event of the year, and it’s spicier than we thought. The new BeQuiet! fans may be the absolute top of the line, but they haven’t avoided certain imperfections that you have to take into account.

Not even BeQuiet! Silent Wings (Pro) 4 avoided comments about being a copy of this or that fan. However, it is important to note that the rotor design, with a greater number of thinner blades with more pronounced leading edge curvature, is what has clearly outperformed traditional designs in efficiency. By those we mean the typical seven-bladed fans with wide blades that hit physical limits.

In short, the previous or say traditional shape of axial rotors, can never outperform the state-of-the-art design that minimizes the relatively inefficient sideways airflow because of the airflow angle, which pushes a large part of the streamlines well off the axial direction of airflow. It’s inefficient because there is more friction between the frame and the blades and hence more noise, which reduces what we call efficiency (the ratio of airflow intensity to noise level).

Sure, blade shape isn’t everything and a lot of things can always go wrong, but what direction fan geometry will take in the coming years is very predictable and understandable. There will be hints of who is copying who for some time to come, but with the gradual demise of traditional rotors, things will calm down and we’ll get used to the “new” ones as the standard. And let’s be glad for that, this is progress in the right direction and it’s just a matter of who can fine tune the small aerodynamic details more effectively. And now let’s break down what and in what quality BeQuiet! has managed to do with Silent Wings (Pro) 4.

The entire surface of the blades is characterized by grooves, which are typical for BeQuiet! and quite useful. In particular, they eliminate microturbulence at the intake, which would be considerably more intense on smooth blades and thus less air would flow through the rotor. Unlike older fans (including the Silent Wings 3), however, these grooves have a slightly shallower depth. This is probably to make the material “weaken” as little as possible in the thinner areas. Still, these are relatively long blades in relation to the width, which are also characterized by higher flexibility.

While it can’t be said that the blades are thin, they are significantly thinner than on the competing Noctua NF-A12x25 fan. In addition, they are made from a material compared to which Noctua presented better properties and lower thermal expansion of “sterrox”. It is a polybutylene terephthalate (PBT) with 30 % glass fibre content to increase sturdiness and reduce the effect of unwanted blade flexing in flight. BeQuiet! admittedly claims that it does not occur, but it does so rather slyly as it refers to maximum speed.

However, the fans also reach critical speeds and resonant frequencies at lower speeds. And this is kind of the case and the biggest negative you’ll have to cope with with Silent Wings (Pro) 4. We’ll go into more detail about what happens, when it happens, and at what intensity in the final chapter, along with how this behavior translates to mechanical vibration in this case.

   

BeQuiet! has shrunk the gap between the ends of the blades and the frame between generations (from 1.2 to 1.0 mm), but it’s still twice the size of the Noctua NF-A12x25 fan that the Silent Wings Pro 4 will be unavoidably compared to. This, too, is a testament to the fact that the BeQuiet! is bluffing and knows that the blades do stretch a bit. As part of some bonus article later on, we’ll try to capture this for you in some macro photos, which show it well with the right lighting.

If the phenomenon described above did not occur, BeQuiet! would definitely reduce the gap as much as possible, while avoiding the possibility of a collision (contact between the blades and the frame). On the other hand, it should be noted that in terms of overall cross-section, there is very little difference between a millimetre and a millimetre and a half gap and it does not dramatically affect performance characteristics. However, it is true that at this level of expensive fans, the overall better/worse performance is built on precisely such small details.

What’s also remarkable about the rotor is the effort of BeQuiet! to maximize the total blade area. When viewed perpendicularly, it is easy to see that the leading edges of the blades are almost exactly above the trailing edges of the previous blades – the gaps are minimal (considerably smaller than on the Noctua NF-A12x25). Now is that good or bad? From a performance standpoint, it’s definitely good. BeQuiet! thus gains a larger surface area into which the air can “lean” while still not abandoning the standard (as for example Phanteks T30) 25 mm thickness.

But then there is the acoustic aspect. But if bringing the leading edges closer to the trailing edges manifested itself most noticeably with a subtle increase in sound intensity around 2.5 kHz, always with a very faint hiss, then all is well and we can conclude that this compromise was worth it.

A big improvement over Silent Wings 3 is in the mounting of the interchangeable corners. SW3 owners know well that the fuse on at least one of the corners has jammed, making it virtually impossible to swap for a different type of corner. However, BeQuiet! did not repeat this mistake and, on the contrary, the new solution is very elegant. There are two latches, and mainly on the outside. The mounting corners are no longer inserted from the side, lengthwise, but directly snap into the fan corner from above. The fixing levers/latches can be conveniently pressed from the outside, thereby removing the particular type of corner and replacing it with another. Assembly and especially disassembly has been improved considerably. Everything works easily and yet holds firmly in place, with no play. So no need to worry about any rattling (typically from unstable joints).

As for the actual corner types, the Silent Wings Pro 4 has up to three. Standard, anti-vibration and corners optimized to work more efficiently on liquid cooler radiators. These are the largest ones, pictured left. Compared to the other types, they increase static pressure on the radiators, and it’s not just a marketing phrase.

The “radiator” corners have both wider and taller arms, which make them fit better with the outer arc of the rotor tunnel. Compared to other types, it seals off any gaps and thus no longer causes unwanted air leaks, which naturally increases the static pressure and thus also increases the overall cooling efficiency, which is also proven in our tests. The radiator corners are pre-installed on the Silent Wings Pro 4, and it should be added that they are only included on fans with “Pro” in the designation. Regular Silent Wings 4’s do not have them and will perform less efficiently on radiators. Admittedly a bit unnecessary, but it’s because BeQuiet! wants to make the more expensive variant of the new fans more attractive.

In a separate test looking at the effect of different corners on fan performance, you’ll also learn that while the “anti-vibration” ones look technically great, they don’t reach their maximum efficiency due to certain collisions. In other words, they don’t completely isolate the vibration from the frame.

However, the advantage of the Silent Wings Pro 4 also lies in other things than the radiator mounting kit. One of these is a more solid cable with a dense fabric braid. Similar to what you’d encounter with mouses or keyboards. In a spot where regular cables break, this one has an extra sturdy intermediate with the BeQuiet! logo.

The justification for the extra 7 EUR over the standard SW4 is also for a speed switch or limiter, which the Silent Wings Pro 4 have in addition. The latter has three stages, where the slowest (M, medium) reduces the maximum speed to about 1575 rpm, the medium (HS, high-speed) to about 2367 rpm and the UHS (ultra high-speed) reaches a maximum of about 2800 rpm.

It is worth noting here that even in a completely non-restrictive (i.e. unbraked) environment, the specified speed is short of 180–200 rpm (but we are still within the allowable tolerance of ± 10 %), which means that the claimed airflow achieved is practically spot-on, even with a small plus margin. This speed switch has the advantage that at lower speeds the PWM control doesn’t drive the speed too high, even on motherboards with more aggressive speed curves.

Starting and minimum speeds remain unchanged across modes at around 620 rpm. That’s perhaps a little more than some users would like, but it’s the toll of that wide range with a super-high top speed. … And we’d almost forgotten that the SW (Pro) 4 (as well as the SW3) also have a 6-pole motor with three-phase torque.

* When reading performance values, a certain amount of tolerance must always be taken into account. For maximum speeds, ±10 % is usually quoted, minimum speeds can vary considerably more from piece to piece, sometimes manufacturers will overlap by as much as ±50 %. This must then also be adequately taken into account for air flow, static pressure and noise levels. If only one value is given in a table entry, this means that it always refers to the situation at maximum speed, which is achieved at 12 V or 100 % PWM intensity. The manufacturer does not disclose the lower limit of the performance specifications in its materials in that case. The price in the last column is always approximate.


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Comments (2) Add comment

  1. Hi. Do you have any idea of why this fan is capped at 2800rpm at 100%PWM speed? I can see in the test results that you are getting 2800rpm max as I do, but do you know why? All three of my fans are capped at 2800rpm.

    1. Obviously this is caused by the limitations of the fan electronics. At 12,00 V (DC/PWM) the approx. 2800 rpm is simply a ceiling. Most of the BeQuiet! fans we have tested do not reach the max. specified speed. They always just fit within the +/- 10 % tolerance. Anyway, we will address your question to BeQuiet! and if we get an answer, we will write it here in the discussion, but the fact is that most fans are a bit faster compared to the parameters and BeQuiet! has it the other way around.

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