Testing Methodology

Although the testing of a cooler appears to be a simple task, there are many factors that need to be considered. 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. However, extracting the absolute thermal resistance of a cooler is no simple task.

The thermal load has to be perfectly even, steady and controllable. The latter is critical as thermal resistance 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 in the thermal load can yield very different results.

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

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

<35dB(A) Virtually inaudible
35-38dB(A) Very quiet (whisper)
38-40dB(A) Quiet (slight humming)
40-44dB(A) Normal (humming noise, comfortable level)
44-47dB(A) Loud* (strong aerodynamic noise)
47-50dB(A) Very loud (strong whining noise)
50-54dB(A) Extremely loud (About equivalent to a typical hairdryer)
>54dB(A) Intolerable for home/office use, special applications only.

*noise levels above this are not suggested for daily use

The Reserator 3 Max Dual AIO CPU Cooler Testing Results, Maximum Fan Speed (12 Volts)
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  • lorribot - Tuesday, August 19, 2014 - link

    You go in to great detail about your test rig and how you test thermal efficiency but completely fail on how you actually test noise, just some " noise measurements are a bit tricky" statement .
    Actually it is not.
    A good test would be the amount of noise produced to cool a given thermal load to say 70C. This would replicate what I would want in the real world, ie how much noise will this thing make cooling my i5/i7 when playing a game or doing massive calculations etc.
    Most noise tests seem arbitrary, such as dB with fans a full speed which is worthless information and provides no useful comparison as all fans run a different speed or are subjective observations of the quality of the noise.
    Noise generated for a number of given workloads would actually be useful please make it happen.
  • Hairs_ - Tuesday, August 19, 2014 - link

    Silent pc review provide this sort of analysis, in an anaechoic chamber, with stock vs. reference fans. However, their db classification for "silent" is different, and liquid coolers always perform worse than a good air cooler on a "cooling per dB" metric.

    SPCR's conclusion (which I'd trust above all others) is that liquid coolers are a bad investment as they cost significantly more, produce worse results and are often far too noisy to justify the results. Push enough air and create enough noise, and you can get all sorts of headline grabbing low temperature results...
  • Gigaplex - Tuesday, August 19, 2014 - link

    While I agree that air cooling is generally preferable to liquid cooling from an audible efficiency perspective, at the extreme overclocking end of the scale, air coolers just can't keep up. Another downside to the massive tower air coolers is that there's greater risk of damaging the system during frequent transportation (eg LAN party users). There are trade-offs either way you go.

    That said, I prefer air cooling as I optimise my systems for noise.
  • AnnihilatorX - Thursday, August 21, 2014 - link

    I disagree. At normal fan speeds liquid coolers tend to lower temperature range and variance, you won't see ultra low temperature, nor you won't see ultra high temperature, and this is due to specific heat capacity of the liquid being higher than air. While overclocked working CPU on air coolers can reach say 70+ deg C, on liquid it would barely reach 40 deg C (speaking from experience) . This is what is important, not low idle temperature.
  • AnnihilatorX - Thursday, August 21, 2014 - link

    To clarify the above reply was replying to Hair not Gigaplex
  • E.Fyll - Wednesday, August 20, 2014 - link

    Actually, it is not as simple as that. Noise measurements are indeed very tricky.

    Your proposed method however is indeed interesting. However, I would need specific equipment to emulate the PWM thermal control of a motherboard and control the coolers in order to maintain a set temperature. I will be adding that in my long "to buy" list.

    I just hope that this will not then start a "comments war" on topics such as "why 150W load and not 160W load", etc etc. :)
  • Impulses - Tuesday, August 19, 2014 - link

    Dunno why we're still obsessed with CPU cooling when must enthusiasts are running GPUs that get far hotter and many are running several of them.

    We really need some sorta standard bracket/mount that could facilitate mounting these things to GPUs... Anand has featured a couple but they all seemed to have issues, or maybe I didn't pay close enough attention.
  • SantaAna12 - Tuesday, August 19, 2014 - link

    Agree in general about GPUS......but....this is a CPU cooler review that anticipates a new line of enthusiast unlocked chips. Right on time perhaps?
  • abhaxus - Tuesday, August 19, 2014 - link

    I have the Kraken G10 mounting a Kuhler 620 to my reference R9 290. I replaced the Kuhler's fan with the stock fan from an H100 and the radiator is mounted in a rigged up location in my case (have it mounted in the 5.25" bays of my Bitfenix Raider). With the fan on low, it is silent and will only hit 90C if I play an extended session of a high GPU usage game (Crysis 3, BF4). With the fan on medium, which is inaudible with music/game audio playing, I never hit over 70C. This is with the card overclocked to 1107/1350 @ +100mv in Afterburner. My VRM temps stay at around 59-65C as well, and I did NOT put VRM sinks on there, just the standard 92mm fan that comes with the G10.

    Very good purchase overall. Now that the Swiftech H220 is back in America I think I will be purchasing one to properly loop my GPU, however.
  • flyingpants1 - Wednesday, August 20, 2014 - link

    I'm totally in agreement, except for the part where you say "many are running several of them". The market for exotic coolers is pretty tiny, and the amount of people who run multiple GPU setups is vanishingly small.

    I'd guess over 90% of PC gamers are using single GPUs under 200 watts, GTX 760 or R9 270x. I'd like to see a slew of water coolers released for those cards.

    The PC market is really, really, reeeeally slow to adapt. It took like 20 years to make USB cables reversible. They're still using ATX, for god's sake. Mini-ITX is nice, but Apple's new Mac Pro slaughters everything from a design standpoint.

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