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 & Conclusion
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  • Klapper.cz - Monday, February 7, 2022 - link

    You don't need to have completely passive system or add CPU fan/multiple case fans as the other "extreme". You just need one almost silent slow-ish (outtake) case fan (ideally 120mm+ and nearby) to make it work just fine and it would be nice to see how it comparatively works in a real case in such (most likely) scenario with more than zero air flow, but still almost as completely passive in a real world sense.
  • Oxford Guy - Monday, February 7, 2022 - link

    Who is ‘you’?

    Fans accumulate dust and are a moving part. Moving parts are a weak point.

    The big issue with passive cooling is the GPU, for gamers.
  • bug77 - Tuesday, February 8, 2022 - link

    The big issue, for me, is that passive cooling works (when it does), because there's some airflow in the case. If everything was passive, that will break down.
    So yes, you may get a passively cooled PSU, maybe even CPU, but probably no more than that.
  • Oxford Guy - Tuesday, February 8, 2022 - link

    Use a mesh or partially open-air case. It is possible to have a fully-passive system.
  • Flunk - Tuesday, February 8, 2022 - link

    A fully open case works much better, but then you have a dust problem.

    Although trying to cool a high-end GPU like a Geforce 3090 with a 350W TDP is a tall order.
  • Spunjji - Wednesday, February 9, 2022 - link

    If you're trying to passively cool a stock 3090 you're doing it a bit wrong, though. If you really needed all that compute power and RAM but silence is important enough to go passive, you'd benefit most by undervolting and sacrificing maybe 10% performance to drop nearly 100W of that TDP.

    It would make sense to go with a more power-efficient prospect in the first place, though. With the current-gen cards that would likely be something like a 6800 / 6800 XT.
  • olde94 - Thursday, February 10, 2022 - link

    It would be a fun engineering task to try and make a 100% passively cooled system for something like a 3090, if we base it off a 250W TDP
  • Oxford Guy - Saturday, February 19, 2022 - link

    olde94, that was the Calyos case that people are still waiting to get in return for the money they put out for them, including the €3,820 copper version.
  • mr_tawan - Thursday, February 10, 2022 - link

    I'd say, put the pc in another room, might be the better option (although it come at cost). Not everyone can have this option, however.
  • sharath.naik - Monday, February 21, 2022 - link

    This is not for cases with any fan. The only use case for passive cooler like this is zero failure tolerance. Not cooling, not dust but have a PC with no moving parts to fail. Honestly there are better solutions for that. So this is kinda a pointless product, that a simple idling fan running at 300rpm will beat in every other use case.

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