Testing Methodology

Although the testing of a cooler appears to be a simple task, that could not be much further from the truth. 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. Extracting the absolute thermal resistance of a cooler however is no simple task, as the load has to be perfectly even, steady and variable, as the thermal resistance also 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 of the thermal load can yield much different results.

Appropriate thermal testing requires the creation of a proper testing station and the use of laboratory-grade equipment. Therefore, 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 the manual control of the testing equipment, the acquisition of the ambient and the in-core temperatures via PT100 sensors, the logging of the test results and the mathematical extraction of performance figures.

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

The noise floor of our recording equipment is 30.2-30.4 dB(A), which represents a medium-sized room without any active noise sources. All of our acoustic testing takes place during night hours, minimizing the possibility of external disruptions.

<35dB(A) Virtually inaudible
35-38dB(A) Very quiet (whisper-slight humming)
38-40dB(A) Quiet (relatively comfortable - humming)
40-44dB(A) Normal (humming noise, above comfortable for a large % of users)
44-47dB(A)* Loud* (strong aerodynamic noise)
47-50dB(A) Very loud (strong whining noise)
50-54dB(A) Extremely loud (painfully distracting for the vast majority of users)
>54dB(A) Intolerable for home/office use, special applications only.

*noise levels above this are not suggested for daily use

The Fractal Design Celsius S24 & S36 AIO Coolers Testing Results, Maximum Fan Speed
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  • HomeworldFound - Friday, June 2, 2017 - link

    The radiators can actually support up to four to six 120mm fans. Beside that it's just another generic boring AIO.
  • sibuna - Friday, June 2, 2017 - link

    why are there no high end air coolers tested in this
  • fixxxer0 - Friday, June 2, 2017 - link


    same test setup here if you want to compare
  • Bulat Ziganshin - Monday, June 12, 2017 - link

    these are upper-middle, but not precisely high-end
  • Bulat Ziganshin - Monday, June 12, 2017 - link

    oh, well. NH-D15 is real supercooler, and its result is only a few degrees worser than results of these FD coolers (with the same noise in low speed mode)
  • Drumsticks - Friday, June 2, 2017 - link

    Thanks for the review. Could y'all do a "best CPU coolers" for the quarter and give some recommendations on each range? With Skylake X and Threadripper coming out, I think it'd be a great time to get a professional opinion. I'm kind of interested in an AIO, but there are quite a lot of choices nowadays.
  • fixxxer0 - Friday, June 2, 2017 - link

    just trying to get a feel for real world thermal loadings vs the standard shown in the test.

    how many watts would a i7 7700 stock under load generate?
  • fixxxer0 - Friday, June 2, 2017 - link

    is it really just the TDP that is advertised for the proc?
  • Drumsticks - Friday, June 2, 2017 - link

    Probably something along the lines of the 60-100 range if you aren't overclocking, but 100-200W range if you overclock depending on how far you go.
  • MrTeal - Friday, June 2, 2017 - link

    It would have been more interesting if you had run the pump at full speed and just varied the fan speed. At full speed this cooler delivered very nice acoustics for its cooling performance. It would have been nice to see how the included fans performed without kneecapping the performance of the pump.

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