By: Jonathan Kwan
May 17, 2013
Let's say you have a large pot of water and a frog. If the water is cold, and you threw the frog in, what would happen? In most cases, the frog will jump out. If we were given the same scenario with boiling water instead of cold water, what would happen? Well, obviously, the frog would die. How about if start with lukewarm water, and then slowly heat it until it reaches the boiling temperature? Contrary to popular belief, the frog will still jump out if it gets hot enough -- Dr. Victor H. Hutchison at the University of Oklahoma conducted this experiment in 2002. Nevertheless, the story of a boiling frog is still an excellent metaphor for us to understand. In order for society to accept change, it must be gradual, and not sudden. In the technology world, it is no different. While the word 'revolution' is thrown around on every product release, most innovation is really evolutionary in nature, with every progress built on the foundation of existing development. Here at APH Networks, we have a long history of reviewing Noctua products. In the past, we have extensively covered their desktop chassis fan line, the Noctua NF-S12 series, as well as its successor, the NF-S12B series. Today, we will once again take a look at Noctua's latest entry into quiet computing. How much of an evolution is the NF-S12A series fans? We took all three variants in, and got down straight to business.
Our review units of the Noctua NF-S12A FLX, NF-S12A PWM, and NF-S12A ULN cooling fans came in a relative small, brown corrugated cardboard box from the company's headquarters in Austria. As always, the package was transferred to Canada Post after making its trip across the pond. I dropped by the postal office soon after receiving the delivery notice in my mailbox to pick them up for our review today. As with last time, we have requested three of each unit for the purposes of evaluation. With a box this small, my first impression called into question with regards to the quantity of each inside. To find out if my suspicions were correct, I grabbed my knife to see what we have inside.
And... yep, someone has missed the note, haha. We have expected three of each model to execute a proper build for testing; unfortunately we ended up with a total of three units, one for each variant. Not good. To roughly reword what we I have said in my NF-F12 PWM and NF-P12 PWM review, this is like having a credit card, but with a $50 credit limit on it. Sure, it is the real thing, but it is not very useful. Oh well!
Moving on, as you can see in our photo above, from the left, we have the NF-S12A FLX, NF-S12A ULN, and NF-S12A PWM, in that order. Its refreshed retail box design was first seen in the NF-P12 PWM last year, and retains Noctua's fundamental color scheme very well, in addition to bringing a modernized appearance. Meanwhile, its specifications, features, and highlights are listed in consistent design with the box on the remaining sides of the retail package. Speaking of which, before we move on, let's dig a little bit more into the details, as obtained from the manufacturer's website:
Noctua NF-S12A FLX
Size: 120x120x25 mm
Connector: 3-pin
Bearing: SSO2
Blade Geometry: S-Series with Anti-Stall Knobs
Frame Technology: AAO (Advanced Acoustic Optimisation)
Rotational Speed (+/- 10%): 1200 RPM
Rotational Speed with L.N.A. (+/- 10%): 900 RPM
Rotational Speed with U.L.N.A. (+/- 10%): 700 RPM
Airflow: 107,5 m³/h
Airflow with L.N.A.: 83,2 m³/h
Airflow with U.L.N.A.: 65,8 m³/h
Acoustical Noise: 17,8 dB(A)
Acoustical Noise with L.N.A.: 10,7 dB(A)
Acoustical Noise with U.L.N.A.: 7,4 dB(A)
Static Pressure: 1,19 mm H2O
Static Pressure with L.N.A.: 0,73 mm H2O
Static Pressure with U.L.N.A.: 0,51 mm H2O
Max. Input Power: 1,44 W
Max. Input Current: 0,12 A
Voltage: 12 V
MTBF: > 150.000 h
Scope of Delivery: Low-Noise Adaptor (L.N.A.), Ultra-Low-Noise Adaptor (U.L.N.A.), 3:4-Pin Adaptor, 30cm Extension Cable, 4 Vibration-Compensators, 4 Fan Screws
Warranty: 6 years
Noctua NF-S12A PWM
Size: 120x120x25 mm
Connector: 4-pin PWM
Bearing: SSO2
Blade Geometry: S-Series with Anti-Stall Knobs
Frame Technology: AAO (Advanced Acoustic Optimisation)
Rotational Speed (+/- 10%): 1200 RPM
Rotational Speed with L.N.A. (+/- 10%): 900 RPM
Min. Rotational Speed (PWM): 300 RPM
Airflow: 107,5 m³/h
Airflow with L.N.A.: 83,2 m³/h
Acoustical Noise: 17,8 dB(A)
Acoustical Noise with L.N.A.: 10,7 dB(A)
Static Pressure: 1,19 mm H2O
Static Pressure with L.N.A.: 0,73 mm H2O
Max. Input Power: 1,44 W
Max. Input Current: 0,12 A
Voltage: 12 V
MTBF: > 150.000 h
Scope of Delivery: Low-Noise Adaptor (L.N.A.), 4-Pin Y-Cable, 30cm Extension Cable, 4 Vibration-Compensators, 4 Fan Screws
Warranty: 6 years
Noctua NF-S12A ULN
Size: 120x120x25 mm
Connector: 3-pin
Bearing: SSO2
Blade Geometry: S-Series with Anti-Stall Knobs
Frame Technology: AAO (Advanced Acoustic Optimisation)
Rotational Speed (+/- 10%): 800 RPM
Rotational Speed with L.N.A. (+/- 10%): 600 RPM
Airflow: 74,3 m³/h
Airflow with L.N.A.: 57,5 m³/h
Acoustical Noise: 8,6 dB(A)
Acoustical Noise with L.N.A.: 6,7 dB(A)
Static Pressure: 0,62 mm H2O
Static Pressure with L.N.A.: 0,44 mm H2O
Max. Input Power: 0,72 W
Max. Input Current: 0,06 A
Voltage: 12 V
MTBF: > 150.000 h
Scope of Delivery: Low-Noise Adaptor (L.N.A.), 3:4 Pin Adaptor, 30cm Extension Cable, 4 Vibration-Compensators, 4 Fan Screws
Warranty: 6 years
Beneath the surface, Noctua's classic internal packaging is sophisticated yet classy as it has always been in the past. I can go on all day about how cool the retail packaging is -- complete with Velcro button flaps and plastic windows for your viewing pleasure -- but I will just be wasting your time. From the left, we have... okay, I have no idea. All of the Noctua NF-S12A variants look exactly the same, so it is practically impossible to tell the difference between them, unless you read the model code printed at the back of each fan. Okay, and visually identify the PWM version by its connector, but this is about it. Sliding out the clear plastic tray from within, it is everything you can come to expect from the Austrian manufacturer of quiet PC components. The fan itself occupies majority of the room, while its accessories are set in the adjacent well. The usual bundle of four vibration dampening mounts is included, but frankly, I have never used them. A properly tightened screw will do the trick. I think Noctua realized this as well, so they have made some modifications to the frame of the NF-S12A cooling fans, as we have first seen in the NF-F12 PWM. This then brings us right into the next section.
Shown in the photo above, from the left, are the Noctua NF-S12A FLX, NF-S12A ULN, and NF-S12A PWM, respectively. All fans appears to be almost physically identical other than the sticker in the middle, which means that it incorporates standard Noctua's color scheme of peach and burgundy-ish brown color. While this is a demonstration of consistency among the whole Noctua fans product line, as well as a trademark Noctua design, stylistically this color scheme may not appeal to everyone. It sure stands out in many windowed cases -- in a positive and negative manner, depending on your perspective -- either way, sometimes, you just have to learn to appreciate tradition.
While I have mentioned their identical physical appearance attributes (Again, other than the sticker in the middle for the user to distinguish between them, as well as the 4-pin header for the PWM model for those who are more observant), if you're anything like me, you probably skipped over the specifications section above -- and just wanted a straight answer on what's the difference between the two products without the technical mumble-jumble. If you are not familiar with Noctua's usual naming scheme, 'ULN' means ultra low noise, as they usually denote in their resistor cable names, while FLX is just a three letter abbreviation 'flex'. PWM stands for 'pulse width modulation', which, as its name suggests, can be driven by a PWM signal for better speed control on newer motherboard models.
With all this in mind, let me give you a straight answer on their differences right now: The NF-S12A FLX has a maximum rotational speed of 1200rpm @ 12V, while the NF-S12A ULN has a maximum rotational speed of 800rpm @ 12V. It's quite logical because the ULN version spins slower, therefore quieter; while the FLX edition can spin at a higher RPM for performance, but undervolted with the included adapters to a lower RPM for quietness -- therefore more 'flexible'. The PWM model is a modified version of the NF-S12A FLX with Noctua's custom-designed NE-FD1 PWM fan driver IC -- hence the name. It has a maximum rotational speed of 1200rpm, just like the FLX edition. Other than that, they are all pretty much the same thing.
This probably explains why there is a slight difference in included accessories between the three Noctua NF-S12A variants. The FLX includes both an LNA (Low Noise Adapter) and an ULNA (Ultra Low Noise Adapter) cable, while the ULN version only includes an ULNA adapter for ultra ultra low noise. Interestingly, the PWM version only includes an LNA adapter. I am very happy to see all cables are finally labeled in plain English by attached tags, rather than color coded as it has been done in the past. To add some class to their products, all cables are fully sleeved out of the box. All NF-S12A variants include a 30cm extension cable out of the box. The non-PWM units come with a Molex to 3-pin adapter, while the PWM model comes with a 4-pin Y-split cable.
The LNA and ULNA adapter brings the Noctua NF-S12A FLX from its 1200rpm maximum to 900rpm and 700rpm, respectively; while the ULNA adapter on the Noctua NF-S12A ULN straps it down to 600rpm from its maximum 800rpm. The LNA adapter on the Noctua NF-S12A PWM caps the maximum RPM from 1200rpm to 900rpm. The NF-S12A PWM has an operating range from 300RPM to 1200RPM in PWM mode. There is no appreciable acoustical noise difference between 700rpm and 600rpm as far as I'm concerned, and very little difference between 900rpm and 700rpm as far as Noctua fans go. We'll go over this in the Tests section in just a short moment. In my opinion, the FLX version should probably accommodates the needs of most quiet PC enthusiasts better than the ULN version. However, if you own computers that support PWM fans, I do not see a reason why you should not buy the PWM variant. PWM signals are vastly superior to voltage control in adjusting the fan speed; this is not to mention it is backwards compatible with 3-pin voltage headers.
One of the biggest challenges to a noise optimized product is to provide a high level of airflow to noise ratio, and even both of these cannot be objectively measured at all times. The most common unit of objective measurement is CFM (cubic feet per minute) of air for airflow, and dB noise, respectively. We will go over how application and CFM is related with regards to its standard measurements, but let's discuss perceived noise first.
dB (Decibels) is a logarithmic unit of sound intensity. While it provides what appears to be an objective measurement for the most part, it should be noted that perceived noise levels to the human ear, and actual sound intensity, could result in very different things. Human ears are more sensitive to particular frequencies, and when those particular frequencies are emitted from its source, it may appear louder than its numbers suggest. That same can be said vice-versa -- frequencies that human ears are less sensitive to can actually have louder dB measurements from a sound meter, yet the human ears does not perceive it to be as loud as the numbers suggest. Other factors such as turbulence noise are often not measured correctly, therefore, while it usually provides a good reference, it does not necessarily reflect real life performance.
With regards to the application and CFM, it is generally optimal to have a fan to have a high air volume flow rate -- but as aforementioned, pure CFM values are limited to an extent with regards to its indication on fan performance. It is not completely about how much air in can move per minute quantitatively, but equally as important is how it is executed in reality. Airflow to noise ratio is an essential factor as mentioned earlier. Static pressure is also very important depending on application. High resistance applications such as dense fins on a large heatsink requires high static pressure as offered by the Noctua NF-P12 PWM and NF-F12 PWM we have reviewed in the past, while case fans needs less static pressure and faster airflow as offered by the Noctua NF-S12A we are reviewing today. Its differences in application is like a large truck that has a diesel engine with lots of low end torque for towing, compared to a sports car with a high revving gasoline engine with lots of power to beat around the track -- they are simply designed for different purposes, so choose one appropriate to your needs.
Now that we are all on the same page, let's get the technical data out of the way first. The NF-S12A FLX and NF-S12A PWM are rated at 63.27 CFM, 17.8 dB, and 0.088 mmHg at 1200RPM, whereas the NF-S12A ULN is rated at 43.73 CFM, 8.6 dB, and 0.046 mmHg at 800RPM. This is a slight improvement over its predecessor. However, if we are just going to look at the Noctua NF-S12A series by specifications alone, then we here at APH Networks will owe everyone who is reading this article a beer. Why? Because, science.
It is the engineering behind the Noctua NF-S12A FLX, NF-S12A PWM, and NF-S12A PWM that makes them acoustically and aerodynamically superior. As an Electrical Engineer, I do not have much experience in this regard besides reading my first year "An Introduction to the Properties of Fluids and Solids" textbook by Robert A. Heidemann, Ayodeji A. Jeje, and Farhang Mohtadi, so I will explain this the best I can, haha. New to the NF-S12A series are what Noctua refers to as the Anti Stall Knobs. In order to achieve higher airflow, the fan's impeller blades have a high angle of attack. The tradeoff with a high angle of attack design is the risk of insufficient airflow over the surface of the blades to continue to generate sufficient pressure for intake air continues to move through. This is because the pressure along the suction side of the asymmetrical blades' trailing edge will gradually decrease as the air flows through. With decreased airspeed and increased counter pressure, air particles will gradually detach from the blade surface, causing flow separation and undesired stalling characteristics. Think of it sort of like the airflow with relation to airspeed over a plane's wings when the angle of attack is beyond the capabilities of the engine's trust. This will cause turbulence in the system, and decrease the performance of the fan.
As such, the new Anti Stall Knobs are placed close to the trailing edges of each fan blade on the impeller. Basically, it is a miniature secondary blade placed on top of the host blade; replicating the asymmetrical surfaces near the end on a smaller scale to increase airspeed. This will rectify the low airspeed phenomena near the trailing edge of the flow pattern; improving its average static pressure and stall margin, and still able to keep the impeller's high angle of attack for higher airflow.
In addition to impeller improvements, Noctua has also implemented frame upgrades first seen in the NF-F12 to the NF-S12A. The Advanced Acoustic Optimization, or AAO Frame, besides having integrated vibration dampeners you have seen in our photos, also features Noctua's Stepped Inlet Design. It carries forward an idea similar to the dimple structure of a golf ball, allowing better airflow attachment to the frame for improved impeller efficiency. Miniature dents inside the fan frame, which the company calls Inner Surface Microstructures, further enhances its performance by creating a smoother and more focused airflow pattern. On the motor side of things, brass metal bearing shells are used on its SSO bearings, so the rear magnet can be placed closer to the rotor axis for more magnetic force. They call this updated SSO implementation SSO2, no surprises here.
Noctua's NE-FD1 PWM IC is the heart of the company's NF-S12A PWM cooling fan. As an Electrical Engineer, this is where I am tempted to dig into what PWM is in detail. Unfortunately, I am sure most of you will fall asleep by the time I finish. Therefore, to make a long story short, a PWM signal used for controlling a fan is basically just a train of rectangular electrical impulses. Each pulse moves from zero to full voltage almost instantaneously, with the fan speed depending on the frequency of signal. The downside of this is it will cause sudden torque impulses in correspondence to the impulse train, which will result in audible clicking noises. To work around this issue, Noctua's NE-FD1 PWM IC integrates their long standing Smooth Commutation Drive technology with their controller chip. In the context of a PWM controller, the transition of each signal impulse is smoothed out, creating a more consistent output of power to the fan's motor, and minimizing irregular noise in the process. The result is more constant torque in the DC brushless motor, and current switching is more consistent to further reduce acoustical noise.
Nerdy details are great. But does it translate accordingly into real life?
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The Tests
Using our tried-and-true APH proprietary 'scientific' method for measuring fan performance we devised back in 2007, it's no surprise that we're using it for this review as well -- we have used it in every fan review since then. While it is not exactly the most objective method you can use (No kidding haha), there's a few attributes of fan performance that we can obtain clearly from our observations: Airflow, airflow consistency, and amount of static pressure generated. It visually portrays characteristics of each fan.
From the left, we have the NF-S12A ULN and NF-S12A FLX spinning at full speed. The NF-S12A PWM is hooked up to a 4-pin motherboard header. Since the NF-S12A PWM is essentially the same thing as the NF-S12A FLX with a PWM IC, I lowered its speed to a lazy 300 RPM to see how it turns out on the other end of the spectrum. As you can see in our tissue paper test above, it is interesting how much the NF-S12A series fans scale with regards to RPM. In the past, you will notice quite a drop in airflow efficiency once you lower the speed. The NF-S12B improved quite a bit, but the NF-S12A easily ellipses its predecessor. The ULN version actually managed to effectively push quite a bit of air through its blades; indicating improved scalability in airflow with speed changes. Obviously, the FLX still moved a lot more air, and the PWM version at 300 RPM barely pushed the tissue up. The FLX and PWM variant at full speed provided tons of airflow as well as relatively adequate static pressure to keep the inside part of the tissue floating, while keeping its end off the ground, thanks to an abundance of fast moving and stable air. As always from Noctua, airflow is very consistent, but I did notice a bit of fluttering. I do not believe the cause of fluttering is a fault in airflow characteristics, but rather, once you have fast enough air, the tissue paper becomes a factor of limitation.
Image taken from another angle, for improved clarity.
Perceived sound is another very important aspect, as we have mentioned earlier with regards to perceived noise versus decibel measurements. However, limitations of this test involves subjective measurement of the reviewer; while one reviewer will tell you it is very quiet, it is entirely plausible that another will claim it is very loud. Throughout the last few years, we have developed our own perceived sound scale to make some objectiveness out of this matter here at APH Networks -- the same measurements are been applied to products ranging from power supplies to video cards. To ensure accuracy, I have several reference devices to make sure my ears are in line at all times. All APH Networks reviewers work on the same scale, so the numbers you see in our reviews are definitely comparable.
Each fan was tested independently in a quiet room, with the power supply isolated, to ensure accuracy. On a scale from 0-10, where 0 is silent and 10 is the loudest, I would rate the Noctua NF-S12A FLX and PWM to be at 2.5/10 at full RPM. For the ULN model, I will place it in at 1.0/10. I simply could not believe what I was seeing -- motor operation was simply unbelievably smooth and was barely audible, even by APH standards. This is at max throttle, too. Thanks to Noctua's NE-FD1 IC on the PWM model, and Smooth Commutation Drive design on all fans, there was no motor clicking noise at all. Even air turbulence noise is kept at a bare minimum. There is a lot of air moving through, but you simply will not hear it. The NF-S12A is ridiculously good. I thought it would be hard for Noctua to do any better than they have in the past, but once again, their unmatched quiet computing products is once again outmatch by themselves. Like, No wai.
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In the conclusion of my Noctua NF-F12 PWM and NF-P12 review last year, I ended with a question-slash-proposition: Where is my NF-S12 PWM? Fast forward to today, here it is, on my desk -- and in all its glory, this is certainly no disappointment. Wait, what? The word "disappointment" should never be used in this review, no matter the context. The Noctua NF-S12A PWM, along with its non-PWM variants, is downright impressive. Sometimes, I feel companies deliberately leave out obvious design features, so they can make an all-new-and-improved version the next year (A certain fruit company does this all the time). Noctua is not one of them. Every time, they make a product that is impeccably awesome, and then with some kind of black magic, makes them even better next year. The NF-S12A series is a perfect example. Delivering efficient airflow and ridiculously low noise, even at full RPM, the Noctua NF-S12A series poses a serious problem not just for its competitors, but also for Noctua themselves: How the heck can you improve this thing? Okay, to be fair, of course it can be improved on, but it will be quite a challenge, haha. As far as individual variants are concerned, if I were to buy one today, it will have to be the NF-S12A PWM. It is backwards compatible, and can be capped to a lower RPM if you need to. The FLX provides some level of flexibility for those who want to hook it up to their power supply directly. Again, I do not see a reason why you would buy the ULN over the FLX, because you can make the FLX a ULN with the included resistor cables, but not the other way around. Either way, the choice is yours -- it is hard to argue against any of them, unless you don’t like the way it looks, which is not even a real reason in my books, haha.
Noctua provided these products to APH Networks for the purpose of evaluation.
Noctua NF-S12A FLX
APH:Renewal Award | APH Review Focus Summary:
8/10 means Definitely a very good product with drawbacks that aren't likely going to matter to the end user.
-- Final APH Numeric Rating is 8.0/10
Please note that the APH Numeric Rating system is based off our proprietary guidelines in the Review Focus, and should not be compared to other sites.
Noctua NF-S12A PWM
APH Recommended Award | APH Review Focus Summary:
8/10 means Definitely a very good product with drawbacks that aren't likely going to matter to the end user.
9/10 means Excellent product with very minor drawbacks that does not affect the overall product.
-- Final APH Numeric Rating is 8.4/10
Please note that the APH Numeric Rating system is based off our proprietary guidelines in the Review Focus, and should not be compared to other sites.
Noctua NF-S12A ULN
APH Review Focus Summary:
7/10 means Great product with many advantages and certain insignificant drawbacks; but should be considered before purchasing.
8/10 means Definitely a very good product with drawbacks that aren't likely going to matter to the end user.
-- Final APH Numeric Rating is 7.2/10
Please note that the APH Numeric Rating system is based off our proprietary guidelines in the Review Focus, and should not be compared to other sites.
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