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 manually. Fans can have significant variations in speed from their rated values, thus their actual speed during the thermal testing is being recorded 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

Introduction & the Cooler Testing Results
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  • A5 - Wednesday, August 25, 2021 - link

    Their redux fans are a bit cheaper and louder than the ones they normally pack with the coolers.
  • Oxford Guy - Wednesday, August 25, 2021 - link

    ‘beautifully designed and made, with the perfectly arranged fins and heatpipes creating a work of art.’

    I’ll call the Louvre.
  • DanNeely - Wednesday, August 25, 2021 - link

    Or maybe just call it the Louver. 🙄
  • AnnonymousCoward - Wednesday, August 25, 2021 - link

    Love the Thermal Resistance vs Sound graph.

    I've been using the NH-U14S for 6 years. I love Noctua quality and honestly don't care what it costs, it's worth it.
  • vegemeister - Wednesday, August 25, 2021 - link

    It's a pity that that y'all don't have the historical data to put other coolers on the R_th vs SPL chart. Every remotely modern fan has PWM control now, and for the ones that don't, motherboards have variable-voltage drive of 3-pin fans. Nobody is bridging their fans between the 12V and 5V supplies anymore.
  • meacupla - Thursday, August 26, 2021 - link

    I get the feeling that, if you are looking to buy an aftermarket heatsink, you should buy the best one.

    You can reuse the heatsink when you upgrade, and a really good one will handle higher wattages just fine.
  • Wrs - Thursday, August 26, 2021 - link

    Though there is no best, I mostly agree, provided the manufacturer is stable and provides long-term support for new sockets. An air cooler should last decades. Stock CPU coolers should go the way of in-box charging bricks; they waste money.
  • damianrobertjones - Thursday, August 26, 2021 - link

    So... lower cost unit usually means that the higher priced items become more expensive. Top, middle and bottom etc. Nice move, Noctua.
  • ZolaIII - Thursday, August 26, 2021 - link

    Meh Noctua isn't really competitive in this segment and probably never will be. My recommendation if you need a plane 4 heat pipe tower cooler (mainstream as it can get) is Artic Freezer 34 CO for some 38$ no cut corners there regarding mont brickets or thermal paste and a blower just a tad worser that best Noctua Industrial (server) ones. On the other hand regular Freezer 34 with standard PO fan (still better than Redux one's) is just 30$.
  • Spunjji - Friday, August 27, 2021 - link

    That does look like a bargain, and I've always had good experiences with their products. Cheers for the tip!

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