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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  • Oxford Guy - Tuesday, February 8, 2022 - link

    Tower coolers designed for very low RPM fans have wider fin spacing. Thermalright’s Macho RT is probably an example. Reply
  • Oxford Guy - Tuesday, February 8, 2022 - link

    Cleaning the dust out of those is no fun. Reply
  • back2future - Wednesday, February 9, 2022 - link

    might be a ~5-7yrs repeating task for 24/7 systems (and low rpm 120/140mm fans)?
    Since fans acoustics found being proportional to around 5th power of rpms, it might fit for some having 240/360mm fans for low rpm :) and airflow is what is needed for heat transfer: Having natural convection around an optimized passively cooled system might get to around 100W heat dissipation an given sizes for case and mainboard clearances and if there's no fan, a passive setup has to create its own 'air flow' speeds. Heat radiation is probably low percentage (with having shiny surfaces?) within device cases anyway? Some utilize ionic wind effects, etc.
    Reply
  • TheinsanegamerN - Thursday, February 10, 2022 - link

    Try 5-7 months. 5-7 years is a 1 way ticket to a system with a coating so heavy you can draw in it. Reply
  • back2future - Wednesday, February 9, 2022 - link

    inspired for searching dust filter for fans, learned that items are available (with intake air flow reduction/resistance mostly not quantified, what might get a future review and compared to passive cooling systems?) Reply
  • shelbystripes - Wednesday, February 9, 2022 - link

    Because a single fan to circulate air through the entire case is optimal for cooling everything inside the case. A heat sink with fan will move heat off the CPU … and around inside the case … still maintaining high ambient temperature inside the case, unless you have a second fan to move air through the case.

    Reducing to a single case can also allow use of a single LARGE case fan (something like 200mm, even) that runs at a low speed, and produces background noise that is less distracting. Smaller fans produce higher pitched buzzing sounds, and have to spin at high speeds to move substantial air; the inverse is also true.
    Reply
  • jmke - Monday, February 7, 2022 - link

    > Finally, we should note that we are testing the NH-P1 in its purely passive form, without any forced airflow at or even near it.

    while you did test the product in an isolated way, giving you excellent values. They are are however not relevant to real world usage. If you install this cooler in your case, near a <500rpm exhaust fan, your system will still be silent and the performance of this cooler will be much better than what your results show here.

    imho an unfair evaluation of a product that's not tested as it will be used.

    like testing 2 cars on a dragstrip, then saying that the Minivan is slower than the Porsche; never mind the fact that real world testing would have had 5 passengers.
    Reply
  • at_clucks - Monday, February 7, 2022 - link

    "near a <500rpm exhaust fan"

    A review for a passive cooler better focus on the worst case scenario: a passive build. Let's not assume someone paying premium for a high end passive cooler will mount other fans in there or place this under the AC.

    You now have the baseline performance and you know putting a 500RPM exhaust fan will improve performance. You'll never worry that the performance is better than expected, you worry when it's worse.
    Reply
  • WaltC - Thursday, February 10, 2022 - link

    I have to agree here. Often a central element to a cooler review is how easy/hard is it to install, and of course how well it works (or doesn't work) when actually installed in a case. I feel like this would have been a royal pain in the derrière to install and test, of course, so I can sympathize with the author on that point. However, that raises the question of why try and review something you will not actually install and test in the environment which said product was designed for? That might be better than beginning a product review with a litany of the things you can't/won't be able to do...;) There are several low-power CPUs that might have been tested, imo, and that might function fine with this passive cooler. AT seems sometimes to shirk testing key elements of reviewed products--an advanced motherboard, for instance, with lots of hardware features was reviewed here. It was the kind of product a n00b would never buy because of its cost and complexity of features. Everything was fine until the review author said he wasn't going to look at the bios controls because, paraphrased, "hardly anyone messes with his bios these days." For that particular motherboard, nothing could be further from the fact of the matter...;) The people who would buy it have every intention of making adjustments according to their preferences in the bios. I would only suggest that AT editorial guidance be more insistence on completeness and thoroughness in the product reviews it publishes. Guesswork and estimations are all fine, but they are no substitute for real testing, imo. Reply
  • Dantte - Monday, February 7, 2022 - link

    That beast is beautiful and is going to look great in my submerge build! Reply

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