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Our testing methods
Our cooling test rig for this review used the following components:

Processor Intel Core i5-6600K
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 MasterAir Pro 3
Cooler Master MasterAir Pro 4
OS Windows 10 Pro

Our thanks to ASRock and G.Skill for their contributions to our test system, and to Cooler Master for providing its heatsinks for testing.

We conduct our heatsink tests on an open test bench. We put each heatsink through the following testing phases:

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

We used the following software in our tests:

  • Prime95 v28.7
  • AIDA64 Engineer v5.80.4000

The ambient temperature in our testing environment was about 70° F (21.1° C).

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

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

At idle, neither of these coolers break a sweat with our Core i5-6600K underneath (nor should they). The MasterAir Pro 4 distinguishes itself under load, however. The larger cooler keeps our stock-clocked CPU running at just 54° C, and it brings the chip most of the way back to its minimum idle temperature after we removed our Prime95 load. While the MasterAir Pro 3 does let the CPU underneath get a bit hotter, its 60° C maximum result under load isn't reason for concern at all. If your goal is to keep a stock-clocked chip cool, both of these heatsinks are up to the job. Budget and size concerns will be the primary reason to choose one over the other.

Even though Intel doesn't include a boxed cooler with its K-series Skylake CPUs, the solid aluminum heatsink from a Pentium G4400 still does a fine enough job of cooling a stock-clocked quad-core CPU. Whether it does that work quietly is another question. Let's take a look at the noise levels these coolers produce under our stock-clocked load.

Noise levels
Here are the idle and load noise numbers we observed with our processor set to its stock speeds. We measured noise levels using the Faber Acoustical SoundMeter application running on an iPhone 6S Plus placed 18" (45.7 cm) from our test system on an open bench. The CPU cooler was the only source of noise from our system.

With a stock-clocked CPU underneath, the MasterAir Pro 4 will appeal to builders looking for a quiet cooler at a fair price. Its 29.8-dBA result at idle will be practically inaudible inside any decent case, and it only produces 31 dBA under load. Those are both excellent results, and I could barely hear the cooler's fan running at idle, much less discern any particular character from it. The Pro 4's 120-mm fan does have a slight baritone quality under load, but it's not annoying.

The MasterAir Pro 3's 92-mm fan has a more complex noise signature. Even at its impressive 29-dBA idle SPL, the Pro 3 has a growly, ticky character that can't be easily ignored. Under load, sound pressure levels increase only a hair to 30.3 dBA, but the fan produces a middle-pitched tonal whir when it speeds up, and the tickiness I could hear at idle also becomes more prominent. Even so, the Pro 3 is a major improvement over today's Intel stock coolers.

Let's take a look at how this duo handles an overclocked CPU now.

Overclocking performance
Seasoned overclockers will already know that the extra performance one can extract from a given chip is a confluence of several variables, most prominent among them the luck of the draw in the silicon lottery. Fancy motherboards and CPU coolers can help to increase the headroom available to a given chip, but they can't increase the overclocking potential baked into a CPU at the foundry. Still, builders should seek to minimize obstacles to overclocking success, and an effective CPU cooler shouldn't stand in the way of reaching the limits of a particular chip.

The MasterAir Pro 4 proved plenty capable of taking our particular Core i5-6600K to its limits. After several rounds of multiplier and voltage increases, we found that our chip was happy at about 1.28V and 4.5 GHz, but no amount of extra voltage made it stable under our Prime95 Small FFTs load at 4.6 GHz. With our final settings in place and its fan running all-out, the MasterAir Pro 4 held our i5-6600K to 76° C, a solid result for the artificial Prime95 torture test.

The Pro 4 produces a respectable 37.2 dBA under that load, as well. That figure may seem impressive on its face, but the MasterFan Pro Air Balance 120-mm spinner on the Pro 4 produces a prominent baritone hum at speed, rather than the broad-spectrum sound quality we'd like from an ideal fan. Thanks to that character, the MasterAir Pro 4 will make itself known in spaces where it's running all-out, even if its absolute sound pressure level isn't that high. If you plan to overclock with this cooler, be OK with sacrificing stealthy operation for performance.

I must admit that I came into our overclocking tests expecting very little from the MasterAir Pro 3. Shows what I know. This tiny terror held our Core i5-6600K to 79° C using the same 4.5 GHz overclock we achieved on the Pro 4. The 92-mm fan on the Pro 3 isn't nearly as nice-sounding at speed as the Pro 4's, though. At full tilt, the 92-mm MasterFan Pro Air Balance sounds like a tiny leaf blower. Its complex noise signature has some tickiness and growliness to it, as well. For overclockers who want to spend as little as possible on their CPU cooler, it seems the Pro 3 is certainly up to the task of some mild to moderate tweaking, but don't expect quiet operation or polite manners at all if you push the chip underneath to its limits.

Conclusions
Cooler Master's MasterAir Pro CPU heatsinks hit most of the marks that good air coolers should these days. The MasterAir Pro 3 offers a much wider PWM range than the Intel stock cooler for quiet running at idle, and the noise character of its 92-mm fan under load is better than the stock heatsink's, as well. Even better, builders who already know how to install an Intel stock heatsink will have no trouble putting the Pro 3 on a motherboard. Most surprisingly, the Pro 3 is a competent cooler for overclocking, as well—at least when paired with a relatively modest CPU like our Core i5-6600K.

The MasterAir Pro 4 continues the bang-for-the-buck legacy of the iconic Hyper 212 Evo, and it brings some nicer cosmetics and a more modern fan to the table. With the right motherboard fan curve, the Pro 4 is practically silent at idle, and it remains quiet under load (although its noise character is a bit more tonal than I would prefer). The MasterAir Pro 4 is a good way to take advantage of the unlocked multipliers of the Core i5-6600K without spending too much cash or adding too much noise to a system's total output, as well.

I have just one major complaint about the MasterAir Pro 4, and it's that Cooler Master didn't take this opportunity to move to a more user-friendly mounting system. While the X-brace system included with the Pro 4 certainly works once it's all in place, other Cooler Master heatsinks offer better-thought-out mounting systems. The Pro 4 does include Intel-style push-pin mounts for those looking for a shortcut, but I'd be wary of using those plastic push-pins with such a large, heavy tower.

Ultimately, builders really can't go wrong with either of these heatsinks. Considering that the $40 MasterAir Pro 3 sells for just $5 less than the $45 MasterAir Pro 4, however, I would imagine most PC DIYers will want the Pro 4 for its quieter fan and extra cooling capacity. Only the most space-constrained microATX or Mini-ITX builders will want to sacrifice those characteristics in favor of the Pro 3's compact size and rougher noise characteristics. Still, both of these coolers are competent within their design constraints, and I'm happy to send them both home with TR Recommended awards.

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