Review: Noctua NF-A4x20 Series fans

We analyzed four Noctua fans, specifically the four NF-A4x20 models, of which two operate at 5V, one being PWM and the 12V models, one is FLX and the other is PWM.

The cooling of systems is very important and today, all technology products often have fans that generate airflow, which helps keep it under control. Normally we talk about large-size fans, at least 120mm, but today we bring you a review of the Noctua NF-A4x20, fans of only 40mm in diameter, which come in four different versions, two of them based on 5V voltages. and two of them based on 12V voltages.

These fans have the characteristic Noctua colors, so they are easily recognizable. Although these colors are unattractive, the Austrian company is the best when it comes to fan manufacturing. These fans implement all the typical technologies of the company's fans, guaranteeing high quality. They have blades with the Flow Acceleration Channels system, which guarantees an efficient air flow, AAO frames, improved to offer the least number of vibrations possible, and SSO2 bearings, which guarantee us great durability and low noise.


This fan has dimensions of 40mm for the fan and a depth of 20mm, which allows it to offer high static pressure, capable of cooling any system. This fan works at a voltage of 5V, so we cannot install it in a system that has a 12V fan output or we will break it. A Zener diode has been installed in these fans, which has the mission of avoiding polarity problems, which would cause the fan to break, which allows it to be protected if it is connected in the wrong way.


We move on to the Noctua NF-A4x20 5V PWM, which is the same as the one we have discussed above, but with the great difference of this fan, it is that it is PWM, so it can operate between 1.100 RPM and 5.000 RPM. Being PWM, it is especially interesting for systems that have this capacity, such as NAS or routers, which require good cooling and tend to have quite bad fans. Like the previous Noctua, this fan cannot be installed in 12V connectors and has a protection system against polarity changes, which allows us to protect the fan if we make a mistake when connecting it.


This Noctua NF-A4x20 FLX is the first of these that works at a voltage of 12V, so we are talking about a more conventional voltage fan, the one normally used in common systems. This fan has a very interesting peculiarity and it is the FLX. FLX technology offers flexibility between operating speeds, operating at 5.000 RPM, 4.400 RPM and 3.700 RPM, to offer a reduced loudness level, when operating at 4.400 RPM and a super reduced loudness level, when operating at 3.700 RPM.


It differs little from the Noctua that we have commented before, but in this case it has the characteristic of being PWM, so it allows operation between 1.200 RPM and 5.500 RPM, but in this case the working speed can be limited to 4.400 RPM, through the LNA system Little more to add with respect to this fan, since it has the typical characteristics of the company's fans, to offer the highest performance and quality.


Fans normally use two systems, bearings and bearings. They both have problems. The bearings are very quiet in their first moments, but wear increases the noise and the useful life of the fans that incorporate them is very short and the bearings make a lot of noise, although they have a fairly long useful life. Noctua has looked for a solution that has a very long useful life and the noise level is minimal and they developed the SSO, a system of self-stabilized bearings of pressurized oil, which has been revised for improvement.

The development of this system is based on its low noise level and the quality demonstrated and tested in many products, in a large number of products. This system is based on an interesting concept of hydrodynamic oil-based bearings that integrate a magnet, which has the function of automatically stabilizing the rotor shaft. Stabilized by a magnetic field, these bearings allow for improved precision and longevity over ball bearing solutions, plain bearings and even traditional hydrodynamic systems.

Noctua has optimized and improved the SSO system in this update called SSO2. Metallic bearings and an injection molding system have been used for this renewed system. They have a magnet closer to the rotor shaft, generating a higher magnetic force on it. It offers, thanks to this system, greater stabilization, precision and durability of the fans.


One of the main problems when operating with fans is that they generate turbulence. These turbulences affect airflows, which is a problem. It usually occurs, above all, in the separation of the delimiting layer on the suction side, in the fan blades, specifically, which causes significant noise due to the vortex and this causes a decrease in energy efficiency due to the flow of the air.

Noctua, to solve this problem, has modified its Noctua A Series fans, with the technology of accelerated circulation channels in the suction part. The arrangement of these channels increases the air flow distribution on the suction side, which improves air flow in the crucial outer regions of the blades. Flow separation is likely to occur when the flow speed in the fan is low, when the fan is operating at low revolutions. Thanks to Flow Acceleration Channels technology, speed is increased, resulting in significantly reduced flow separation, which reduces noise in the vortex and improves airflow efficiency.


The Focused Flow Frame has been designed to obtain improved performance in applications that require increased pressure, such as heatsinks and radiators. This frame has eleven blades that straighten, channel and direct the airflow, allowing the NF-F12 fans, which allows these fans to compete in performance against conventional fans when operating at high speeds.

These blades of the NF-F12, are arranged in a variable angular distance and have the Vortex-Control Notches system, notches in the fan that improve the control of the air vortex. This allows to improve the distribution of the sound emission in a wide spectrum of frequencies, which makes the noise of this fan more pleasant to the human ear.

As the stator blades move, the fan blades create pressure pulses. This interaction between the rotor and the stator contributes significantly to the overall emission of the fan noise. The uniform distribution of the blades, the relatively geometric constellation of the rotor blades, and the blades are identical each time the rotor moves to the next blade. When one of the rotor blades passes one of these blades, the same pressure pulses are created.

These period pulses, acoustically, produce fewer sounds at different frequencies that are manifested in frequency peaks within the acoustic spectrum of the fan, which provides a more distinguishable and tonal character. Noctua, to minimize this phenomenon, the blades of the NF-F12 have a variable angular distance between 31º and 37º. This measure causes the geometric situation between the parts of the rotor and the stator to be slightly different each time the rotor moves over the next blade, which generates aerodynamically different pressure pulses. This allows a reduction in sound that is distributed over a wide frequency range. Generating an acoustic profile with a wider bandwidth and less tonal, the vanes in variable angular distance, make this fan more pleasant to the human ear and mix more efficiently with the background noise.

This technology was first implemented in a NF-P12 ventilator. These vortex control samples are aerodynamically designed measurements for two different purposes: the first is the vortex control notches causing the air flow to pass through the suction and pressure side of the mixing blades or blades. more easily at the end of the shaft, which allows a reduction in turbulence and a reduction in speed loss. It allows the fan an increase in the higher energy frequency and a reduced noise emission.

The second improvement is based on the vortex control notches, which make the acoustic profile of the fan more pleasant to the human ear. Thanks to these notches, the vortices are reduced, each generating slightly different tones. This is due to the effect that they have a variable angular distance from the blades, insofar as the sound emission is better distributed over a broader spectrum of frequencies and this makes it possible to reduce the frequency peaks. This sound pattern is perceived by the user in a way that is much less disturbing and pleasing to the human ear.


These Noctua fans are designed to be as quiet as possible and that is why an AAO frame has been manufactured for them. The advanced acoustic optimization framework has built-in anti-vibration pads, as well as a step-by-step input design and internal surface microstructures, developed by Noctua, leading to a further improvement in energy efficiency and performance. fan performance.


The fans of this professional series have been designed step by step type. This allows Noctua an advanced measure of aerodynamic design first introduced in the NF-F12 fans. This allows adding turbulence to the air inlet of the fan, designed in a step-by-step system that facilitates the transition from laminar to turbulent flow. This measure has an effect very similar to the external structure of golf balls, which allows an improvement in the attachment of the flow of the frame, which allows the impulsion when more air is introduced and therefore, improves the overall efficiency of the air flow.

These improvements offer some aerodynamic improvements, which has a step-by-step input design, which also reduces input tonal noises caused by the input of a laminar flow. Thanks to this modification in the turbulent flow design, it produces a noise profile with a higher bandwidth. Thanks to this improvement in the design of the step-by-step entrance, it contributes to the improvement of the acoustic qualities of said fan, which allows it to integrate better with background noise and be more pleasant to the human ear.


The Noctua NF-A4x20 fans, in their four versions, are only 40mm, thinking not only of compact systems with small dimensions, but also of NAS and routers, which tend to implement poor quality fans, very noisy and that they usually last a short time. These fans are characterized by being of excellent quality, as it cannot be otherwise as they are from Noctua and they offer a great air flow, everything you can ask for in a fan.

Offering a good airflow is very important and NAS and router systems tend to lose cooling, so it is very important to have a good fan. The cooling of these components is normally very bad and therefore, it is necessary to improve with high efficiency fans that offer a great air flow. Especially these components tend to suffer in summer, which is when you need more power and a great flow of air.

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