Testing Methodology

Although the testing of a cooler appears to be a simple task, there are many factors that need to be considered. Proper thermal testing cannot be performed with a cooler mounted on a single chip, for multiple reasons. Some of these reasons include the instability of the thermal load and the inability to fully control and/or monitor it, as well as the inaccuracy of the chip-integrated sensors. It is also impossible to compare results taken on different chips, let alone entirely different systems, which is a great problem when testing computer coolers, as the hardware changes every several months. Finally, testing a cooler on a typical system prevents the tester from assessing the most vital characteristic of a cooler, its absolute thermal resistance.

The absolute thermal resistance defines the absolute performance of a heatsink by indicating the temperature rise per unit of power, in our case in degrees Celsius per Watt (°C/W). In layman's terms, if the thermal resistance of a heatsink is known, the user can assess the highest possible temperature rise of a chip over ambient by simply multiplying the maximum thermal design power (TDP) rating of the chip with it. However, extracting the absolute thermal resistance of a cooler is no simple task.

The thermal load has to be perfectly even, steady and controllable. The latter is critical as thermal resistance varies depending on the magnitude of the thermal load. Therefore, even if it would be possible to assess the thermal resistance of a cooler while it is mounted on a working chip, it would not suffice, as a large change in the thermal load can yield very different results.

Appropriate thermal testing requires the creation of a proper testing station and the use of laboratory-grade equipment. To accomplis this, we created a thermal testing platform with a fully controllable thermal energy source that may be used to test any kind of cooler, regardless of its design and/or compatibility. The thermal cartridge inside the core of our testing station can have its power adjusted between 60 W and 340 W, in 2 W increments (and it never throttles).

Furthermore, monitoring and logging of the testing process via software minimizes the possibility of human errors during testing. A multifunction data acquisition module (DAQ) is responsible for the automatic or manual control of the testing equipment, the acquisition of the ambient temperature, and the in-core temperatures via PT100 sensors. It also handles the logging of the test results and the mathematical extraction of performance figures.

Finally, as noise measurements are a bit tricky, their measurement is only performed manually. Fans can have significant variations in speed from their rated values, thus their actual speed during the thermal testing is acquired via a laser tachometer. The fans (and pumps, when applicable) are powered via an adjustable, fanless desktop DC power supply and noise measurements are taken 1 meter away from the cooler, in a straight line from the fan engine.

At this point we should also note that the Decibel scale is logarithmic, which means that roughly every 3 dB(A) the sound pressure doubles. Therefore, the difference of sound pressure between 30 dB(A) and 60 dB(A) is not "twice as much" but nearly a thousand times greater. The table below should help you cross-reference our test results with real-life situations.

<35dB(A) Virtually inaudible
35-38dB(A) Very quiet (whisper)
38-40dB(A) Quiet (slight humming)
40-44dB(A) Normal (humming noise, comfortable level)
44-47dB(A) Loud* (strong aerodynamic noise)
47-50dB(A) Very loud (strong whining noise)
50-54dB(A) Extremely loud (About equivalent to a typical hairdryer)
>54dB(A) Intolerable for home/office use, special applications only.

*noise levels above this are not suggested for daily use

The Reserator 3 Max Dual AIO CPU Cooler Testing Results, Maximum Fan Speed (12 Volts)
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  • bludragon - Wednesday, August 20, 2014 - link

    So really what we need is testing using a real cpu since getting heat off the die is the biggest issue with Haswell and I assume the current AMD cpus. It would be good to see that with a stock cpu, and one that has been delidded and had the stock tim replaced with liquidpro. I expect most decent coolers will actually perform within a very similar and narrow range without the delid. I don't know what happens with the delid...
  • garadante - Thursday, August 21, 2014 - link

    Though I beg to pose the question that, if C/W is so important for someone reading these numbers, is it so unreasonable to assume that they may be seriously interested in using fans or thermal paste different from those included in the stock product? Which is one of my primary points in my comments. Testing CLCs 100% stock is useful for a certain segment of the audience but just that, a segment. Those users who care enough about performance to look into a CLC but not those who care enough to do the small extra steps necessary to eke even better performance out of an expensive piece of processor cooling equipment. I argue that the people who care about using better fans and better thermal paste are the same people who care about a radiator's C/W performance. And including a section of the review that looks at the performance of even a subset of these CLCs on actual CPUs would give a valuable contrast for the readers who don't realize the results here on useless in actual applications short of comparing radiators in a controlled environment. A section that says, "Hey, these are the best CLCs from the review but on this and that CPU at stock and such and such overclock the delta T is this. Therefore understand that you cannot use the results here to target a desired temperature for your own setup because there are so many variables. The results of this review simply allow you to choose a CLC based on its merits relative to other CLCs in a high controlled, synthetic environment. You might need research elsewhere if you're trying to hit 60 C Prime95 temperatures on your 4790K running at 4.7 GHz."
  • AnnihilatorX - Thursday, August 21, 2014 - link

    That's actually pretty easy to calculate base on C/W.

    4790k has maximum TDP of 88W, if a cooler has a C/W of 0.07, the cooler would be able to approximately cool the CPU to 6.16 deg C above ambient. You can see the numbers add up by comparing the different thermal watts in the graph "Core Temperature, Constant Thermal Load" and multiplying that with the respective C/W.
  • garadante - Thursday, August 21, 2014 - link

    You fail to recognize my points. In the real world any of these CLCs with a C/W of 0.07 or even lower would be lucky to achieve a delta T of 40 with a 4970k at 4.7 GHz. Because there are many more factors involved regarding the temperature of a CPU core. Where the core is located relative to the best contact area between the heatsink and the IHS, what type of TIM is used between the die and the IHS, the IHS and the heatsink. These are things that can only be seen using an actual CPU which is my whole point. It seems that E.Fyll has tricked you into thinking his C/W numbers are at all meaningful in a real application. They serve one purpose and one purpose only: comparing the relative performance of CLCs. But that's easy enough to see just looking at the wattage temperature graphs. No use in making a function out of the results unless you want to know how a CLC would handle under a 1000 watt load on this specific testing rig.
  • garadante - Thursday, August 21, 2014 - link

    And testing with consistent fans across all radiators would give much more useful results when seeing the merits of each radiator. Fans are cheap and it's very reasonable to assume quite a few people would be interested in using aftermarket fans, -if- the performance gains are there, which is my whole point. The Cooler Master Nepton 280L looks good at first when you look solely at the temperature results, but then you look at the fan RPM and dB rating. The Corsair H110 uses a significantly slower and quieter fan but comes within a degree or two delta T of the 280L. Therefore Cooler Master likely uses very noisy, inefficient fans where Corsair uses much more efficient fans and quieter ones at that without sacrificing too much performance. Throw on the same fans on both and you remove that difference and you can see which radiator itself (where your money's going) actually is superior (or at least superior with higher CFM or higher static pressure or a mixture, etc, where E.Fyll coming up with an approximate function would actually be useful).
  • BillyONeal - Wednesday, August 20, 2014 - link

    Great article. It would be nice to see Noctua's NH-D14 or NH-D15 for a comparison with a good air cooler.
  • bludragon - Wednesday, August 20, 2014 - link

    I second that
  • C'DaleRider - Wednesday, August 20, 2014 - link

    Here you go......(hint) It's in the Bench.

  • bludragon - Wednesday, August 20, 2014 - link

    Thanks! I had forgotten about that. Only... looking at the results there the temps are not comparable to this article. Is there a post anywhere about the testing methodology for CPU coolers in bench? And yes, I did search...
  • E.Fyll - Wednesday, August 20, 2014 - link

    There will be many reviews of air coolers coming up. As they will be tested using the exact same procedure, the results will be directly compared to those of this review (and every cooling-related review that I perform).

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