Testing Methodology

Although the testing of a CPU cooler appears to be a simple task, that could not be much further from the truth. For multiple reasons proper thermal testing cannot be performed with a cooler mounted on a single chip. 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 (though human perception is itself also not linear). 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 Corsair H80i GT and H100i GTX Testing Results, Maximum Fan Speed (12 Volts)
POST A COMMENT

47 Comments

View All Comments

  • zeeBomb - Monday, November 16, 2015 - link

    I came for the coolers. I wanna stay COOL. Reply
  • Der2 - Monday, November 16, 2015 - link

    A cooling system is essential for a great PC build. Reply
  • ShortWicky - Monday, November 16, 2015 - link

    Brilliant deduction Einstein, do go on with more glimmers of genius insight Reply
  • Black Obsidian - Monday, November 16, 2015 - link

    Fyll, it's possible that you've covered this before, but in cases where AIO coolers have the same heatsink/block unit as these two do, is the absolute thermal resistance essentially measuring the effectiveness of their radiators and fans, or are there other potential variables to consider?

    I'm guessing, for instance, that the days of significant variations in the quality of machining of the heatsink contact surface are long over? If I never have to lap another heatsink, it'll be too soon...
    Reply
  • basroil - Monday, November 16, 2015 - link

    Thermal resistance is affected by:
    1) Overall sink and radiator design
    2) Fluid flow rate
    3) Fluid type (not much change since all use basically the same thing)
    4) Fan speed and efficiency
    5) Mounting pressure
    6) Thermal paste quality

    Assuming 1-3 are identical (because of OEM designs), it's fan and paste performance and mounting pressure you see change thermal conductance
    Reply
  • nathanddrews - Monday, November 16, 2015 - link

    What AIO coolers have the quietest pumps (least whine)? Reply
  • rpjkw11 - Monday, November 16, 2015 - link

    Nothing in this review shows a need to replace my Noctua NH-D15, cooling an i7 5960X @ 4.3 and an Asus STRIX GTX 980Ti. I'm having absolutely no problem with heat or air flow. One of these days I'll take the plunge and try a water AIO, but this ain't the day.

    Thanks for the great review!
    Reply
  • shaolin95 - Monday, November 16, 2015 - link

    So if "I'm having absolutely no problem with heat or air flow" then why did you read this whole thing for? ;)
    I much rather have an AIO for a clean look, easier to clean than a big air cooler and trust me...I used to love them! I had the D14 with 3 massive fans AND shrouds before. I started the thread for it in case you are curious how it used to look:
    http://www.overclock.net/t/628569/official-noctua-...

    Not saying that Air coolers are not good...the D15 is the top in my list but I prefer AIO.
    Reply
  • Chaitanya - Monday, November 16, 2015 - link

    A good air cooler is still better than most of the entry level/mid segment AIOs. AIOs have a copper heat plate and aluminium radiator, couple that with non-refillable system you might face a failed pump due to corroded metal. If you want an AIO better be ready to spend on likes of Swiftech/EKWB one as they don't mix metals together in the system and are user serviceable and expandable. Reply
  • Morawka - Tuesday, November 17, 2015 - link

    AIO are disposable.. you use then for 3-5 years then that's it, 50% water has evaporated. You could open it up, but good luck with that. Reply

Log in

Don't have an account? Sign up now