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Our testing methods
Here are the specifications of our test system:

Processor Intel Core i7-6700K
Motherboard ASRock Z170 Extreme7+
Memory 16GB G.Skill Trident Z DDR4-3000 (2x8GB)
Graphics card None
Storage Kingston HyperX 480GB SSD
Power supply SeaSonic SS-660XP2
CPU cooler Cooler Master MasterLiquid Pro 240
Cooler Master MasterLiquid Pro 280
Cooler Master MasterAir Pro 4
OS Windows 10 Pro

Our thanks to ASRock and G.Skill for their contributions to our testing system, and to Cooler Master for providing the heatsinks we used in this review. We'll be using Cooler Master's own MasterAir Pro 4 heatsink as a point of comparison for these liquid coolers.

Our heatsink testing cycle comprises the following phases:

  • 10 minutes idling at the Windows 10 desktop
  • 20 minutes running the Prime95 Small FFTs CPU torture test
  • 10 minutes idling at the Windows 10 desktop

We used the following software in our tests:

Cooling performance
Here are the results of our cooling tests, plotted over time:

And here are the minimum and maximum temperatures reached during each testing phase:

With a stock-clocked Core i7-6700K underneath, both of these coolers are more than up to the task of keeping the CPU cool. The MasterLiquid Pro 280 only cuts a degree off the Pro 240's maximum load temps, but both liquid coolers are doing a better job than the MasterAir Pro 4 and its single 120-mm fan. Let's see how much noise the liquid coolers produce while they're doing their thing.

Noise levels
Here are the noise levels we recorded for each cooler at idle and under load. We collected this data using the Faber Acoustical SoundMeter app running on an iPhone 6S Plus. Each measurement was taken 18" from each cooler.

At idle, the only sound from either of these coolers will be the quiet (but still noticeable) noise from the pump heads on these coolers. Both MasterFan variants are practically inaudible at idle. That said, they're still ever-so-slightly louder than the MasterAir Pro 4 and its pump-free tower.

With a stock-clocked load underneath, the MasterLiquid Pro duo sets itself apart from the MasterAir Pro 4. Compared to the air cooler's 43.4 dBA result, the MasterLiquid Pro 240 shaves off an impressive 7.6 dBA, and the MasterLiquid Pro 280 is a whopping 8.9 dBA quieter. Going by the rule of thumb that a 10 dBA increase results in a perceived doubling of loudness, these coolers both deliver an impressive and immediately noticeable reduction in load noise compared to the MasterAir Pro 4.

Of course, absolute noise levels are just one characteristic of the perceived loudness of a cooler. Subjectively, the Pro 240's 120-mm spinners sound excellent while cooling a stock-clocked CPU. They make next to no perceptible noise at idle, and their largely broad-spectrum noise character under load is only disturbed by a slight high-midrange tonal whir.

For builders who want an even quieter-sounding cooler, the MasterLiquid Pro 280 is the undeniable champion in our tests. Like its 240-mm counterpart, the Pro 280's fans are practically inaudible at idle, but they maintain a soft and pleasant broad-spectrum character under load.

Despite Cooler Master's re-engineered "silent driver" in the pumps of these coolers, the MasterLiquids both produce a soft but noticeable whir at idle. We tested both pumps at full speed, but unlike the Neptons before them, the MasterLiquids seem to have a bit of PWM range built into their pumps, so it might be possible to quiet them down even more under light load with the right fan curve. Even so, Cooler Master's new pump isn't obtrusive-sounding, and it'll probably be next to inaudible in a case.